Implement support for Forgejo projects

[lbarcziova]

• implement related methods in service
• implement methods for the class inheriting from GitProject
  • methods for permission handling and info will be implemented separately (Implement support for Forgejo project permissions #878)
  • follow how the methods are implemented in other services, i.e. if possible, leave the implementation to be done on specific objects and only specify the @indirect decorator
• use functionality from https://codeberg.org/harabat/pyforgejo/src/branch/main/pyforgejo/api/repository

Client usage docs: https://codeberg.org/harabat/pyforgejo#usage

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Part of #866