Support exposing capabilities and settings
On a smart proxy feature listing, we can only get a set of named features, but features can't have optional functionality or provide any other information to the foreman server.
Refs #25614 - Expose settings from the correct layer
Before this change every expose_setting would only be read from the
This changes makes sure that a provider can expose settings from its own
config file. For example, puppetca exposes from puppetca.yml and
puppetca_http_api exposes from puppetca_http_api.yml.