Merge Puppet Proxy Puppet API provider code into the Puppet module
In #26591 the legacy provider was dropped. Since then, there is only one provider. The provider code was kept since it didn't need any changes to configuration files. However, having a module with just a single provider is complex. Both from a code perspective and as an admin.
The implications are that the puppet.yaml and puppet_proxy_puppet_api.yaml files are merged (after being split in #13667). This means installer and manual updates are needed to reflect this.