[PP-1] Consider moving some of Package Manager's config options to settings

Which config options are being considered here?

These are the current settings:

executables:
  composer: ~
  rsync: ~
additional_trusted_composer_plugins: []
include_unknown_files_in_project_root: false

The composer and rsync executables could be environment specific, so for me those should definitely move to settings.php to avoid people having to use $config overrides in settings.php (which is less obvious than $settings).

The other two also seem like they could be environment specific potentially.