Add init command

[p1gp1g]

No description provided.

[obfusk]

Thanks!

Sadly, I don't currently have time to review this and get it into proper shape to be merged, but I will definitely look at it when implementing the init command and suggestions and feedback are always appreciated even if it may take a while for me to get to them.

My main focus right now is to spend my limited time on getting feedback on basic functionality (not "nice to have" things like init that are not essential for power users willing to help test during the current alpha status), focusing solely on fixing any bugs people may find and implementing missing metadata functionality based on real-world needs and feedback. Testing and feedback for that would be very much appreciated :)

This will then be followed by things like JSON schemas to lint the YAML to ensure users get proper feedback on invalid configuration files, and more advanced features like integration with other tooling, followed by "nice to have" things like init to make it easier to set up a repo.

Also, the init command was intentionally left unimplemented for now in part to avoid making similar design mistakes as fdroidserver (e.g. resulting in people ending up with an unexpected DN they can't change later).