We implementated the Extensions plugin (previously Marketplace) with the goal to make it an upstream plugin. To implement the plugin in time we developed it in rhdh-plugins. The primary goal of this feature is to move the code to the backstage/community-plugins repo (without any dependencies to RHDH).

ACs

1. Cleanup / improve the techdocs
2. Make all path variables and catalog imports (providers) optional
3. Check that the plugin works fine on pure backstage. Fix issues if needed.
4. Move the main code base for the extensions plugin to BCP (without any RHDH specific code)
5. Keep RHDH specific code in rhdh-plugins and extend the BCP code base, if needed