During the db:migrate I ran into this problem:

# foreman-rake db:migrate --trace
** Invoke db:migrate (first_time)
** Invoke db:load_config (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:load_config
** Invoke plugin:refresh_migrations (first_time)
** Invoke environment 
** Execute plugin:refresh_migrations
** Execute db:migrate
== 20200602155700 DropPuppetRun: migrating ====================================
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

Setting::Puppet is marked as readonly
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/persistence.rb:963:in `_raise_readonly_record_error'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/persistence.rb:532:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/callbacks.rb:309:in `block in destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/callbacks.rb:101:in `run_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/callbacks.rb:825:in `_run_destroy_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/callbacks.rb:309:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:310:in `block in destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:375:in `block in with_transaction_returning_status'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:278:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:212:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:366:in `with_transaction_returning_status'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:310:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/relation.rb:544:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/relation.rb:544:in `destroy_all'
/usr/share/foreman/db/migrate/20200602155700_drop_puppet_run.rb:3:in `up'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:831:in `exec_migration'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:812:in `block (2 levels) in migrate'
/opt/rh/rh-ruby25/root/usr/share/ruby/benchmark.rb:293:in `measure'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:811:in `block in migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:471:in `with_connection'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:810:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1002:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1310:in `block in execute_migration_in_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1361:in `block in ddl_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:280:in `block in transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/transaction.rb:280:in `block in within_new_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:26:in `block (2 levels) in synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `handle_interrupt'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `block in synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `handle_interrupt'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/transaction.rb:278:in `within_new_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:280:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:212:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1361:in `ddl_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1309:in `execute_migration_in_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1281:in `block in migrate_without_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1280:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1280:in `migrate_without_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1229:in `block in migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1382:in `with_advisory_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1229:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1061:in `up'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1036:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/tasks/database_tasks.rb:238:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:86:in `block (3 levels) in <top (required)>'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:84:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:84:in `block (2 levels) in <top (required)>'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `block in execute'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `each'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `execute'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:195:in `block in invoke_with_call_chain'
/opt/rh/rh-ruby25/root/usr/share/ruby/monitor.rb:226:in `mon_synchronize'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:188:in `invoke_with_call_chain'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:181:in `invoke'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:160:in `invoke_task'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `each'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `block in top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:125:in `run_with_threads'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:110:in `top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:83:in `block in run'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:186:in `standard_exception_handling'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:80:in `run'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/exe/rake:27:in `<top (required)>'
/opt/rh/rh-ruby25/root/usr/bin/rake:23:in `load'
/opt/rh/rh-ruby25/root/usr/bin/rake:23:in `<main>'

Caused by:
ActiveRecord::ReadOnlyRecord: Setting::Puppet is marked as readonly
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/persistence.rb:963:in `_raise_readonly_record_error'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/persistence.rb:532:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/callbacks.rb:309:in `block in destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/callbacks.rb:101:in `run_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/callbacks.rb:825:in `_run_destroy_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/callbacks.rb:309:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:310:in `block in destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:375:in `block in with_transaction_returning_status'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:278:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:212:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:366:in `with_transaction_returning_status'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:310:in `destroy'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/relation.rb:544:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/relation.rb:544:in `destroy_all'
/usr/share/foreman/db/migrate/20200602155700_drop_puppet_run.rb:3:in `up'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:831:in `exec_migration'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:812:in `block (2 levels) in migrate'
/opt/rh/rh-ruby25/root/usr/share/ruby/benchmark.rb:293:in `measure'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:811:in `block in migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:471:in `with_connection'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:810:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1002:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1310:in `block in execute_migration_in_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1361:in `block in ddl_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:280:in `block in transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/transaction.rb:280:in `block in within_new_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:26:in `block (2 levels) in synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `handle_interrupt'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `block in synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `handle_interrupt'
/opt/theforeman/tfm/root/usr/share/gems/gems/activesupport-6.0.3.1/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `synchronize'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/transaction.rb:278:in `within_new_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/connection_adapters/abstract/database_statements.rb:280:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/transactions.rb:212:in `transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1361:in `ddl_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1309:in `execute_migration_in_transaction'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1281:in `block in migrate_without_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1280:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1280:in `migrate_without_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1229:in `block in migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1382:in `with_advisory_lock'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1229:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1061:in `up'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/migration.rb:1036:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/tasks/database_tasks.rb:238:in `migrate'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:86:in `block (3 levels) in <top (required)>'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:84:in `each'
/opt/theforeman/tfm/root/usr/share/gems/gems/activerecord-6.0.3.1/lib/active_record/railties/databases.rake:84:in `block (2 levels) in <top (required)>'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `block in execute'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `each'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:251:in `execute'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:195:in `block in invoke_with_call_chain'
/opt/rh/rh-ruby25/root/usr/share/ruby/monitor.rb:226:in `mon_synchronize'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:188:in `invoke_with_call_chain'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/task.rb:181:in `invoke'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:160:in `invoke_task'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `each'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:116:in `block in top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:125:in `run_with_threads'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:110:in `top_level'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:83:in `block in run'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:186:in `standard_exception_handling'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/lib/rake/application.rb:80:in `run'
/opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.0/exe/rake:27:in `<top (required)>'
/opt/rh/rh-ruby25/root/usr/bin/rake:23:in `load'
/opt/rh/rh-ruby25/root/usr/bin/rake:23:in `<main>'
Tasks: TOP => db:migrate

Where I have this slightly outdated config, now that we mention it: updating those files is a major pain, perhaps running the foreman-installer before running vimdiff would be better?

---
### File managed with puppet ###
## Module:           'foreman'

:unattended: true
:require_ssl: true
:locations_enabled: false
:organizations_enabled: false
:puppetrun: false

# The following values are used for providing default settings during db migrate
:oauth_active: true
:oauth_map_users: false
:oauth_consumer_key: xxxxxxxxxxxxxxxxxx
:oauth_consumer_secret: xxxxxxxxxxxxxxxx

# Websockets
:websockets_encrypt: true
:websockets_ssl_key: /etc/puppetlabs/puppet/ssl/private_keys/theforeman.example.com.pem
:websockets_ssl_cert: /etc/puppetlabs/puppet/ssl/certs/theforeman.example.com.pem

# SSL-settings
:ssl_certificate: /etc/puppetlabs/puppet/ssl/certs/theforeman.example.com.pem
:ssl_ca_file: /etc/puppetlabs/puppet/ssl/certs/ca.pem
:ssl_priv_key: /etc/puppetlabs/puppet/ssl/private_keys/theforeman.example.com.pem

# HSTS setting
:hsts_enabled: true

# Log settings for the current environment can be adjusted by adding them
# here. For example, if you want to increase the log level.
:logging:
  :level: info
  :production:
    :type: file
    :layout: pattern

# Individual logging types can be toggled on/off here
:loggers:

# Foreman telemetry has three destinations: prometheus, statsd and rails log.
:telemetry:
  # prefix for all metrics
  :prefix: 'fm_rails'
  # prometheus endpoint is at /metrics
  # warning: ruby client library currently does not supprt multi-process web servers
  :prometheus:
    :enabled: false
  # works with statsd_exporter too, use the rake task to generate config
  :statsd:
    :enabled: false
    # IP and port (do not use DNS)
    :host: '127.0.0.1:8125'
    # one of 'statsd', 'statsite' or 'datadog'
    :protocol: 'statsd'
  # Rails logs end up in logger named 'telemetry' when enabled
  :logger:
    :enabled: false
    # logging level as in Logger::LEVEL
    :level: 'DEBUG'

:dynflow:
  :pool_size: 5
  :redis_url: redis://localhost:6379/6

:rails_cache_store:
  :type: file

# Configure reverse proxy headers
:ssl_client_dn_env: HTTP_SSL_CLIENT_S_DN
:ssl_client_verify_env: HTTP_SSL_CLIENT_VERIFY
:ssl_client_cert_env: HTTP_SSL_CLIENT_CERT
:authorize_login_delegation: true
:authorize_login_delegation_auth_source_user_autocreate: External

I got support from tbrisker on freenode and we had this discussion:

16:02   tbrisker| Han: delete line 10
16:02   tbrisker| Han: you can also delete lines 8-9 while there, they have no affect for a while now :)
16:03   tbrisker| Han: did you upgrade using the installer?
16:04        Han| No I followed the manual on upgrading. But managing those diffs from the new config formats is a pain. It's not explained at all.
16:05        Han| Yay! the migrate pulled through! Thanks!
16:07   tbrisker| Han: i think the installer should update that file for you, normally you wouldn't need to manual edit it
16:08   tbrisker| Han: can you open an issue for this though? the migration shouldn't fail anyways even if the setting was set manually
16:08        Han| The manual tells me to run the installer after the vimdiff steps.
16:08        Han| Sure. Gladly.