feat: Support for other git forges like a forgejo, gitea and sourcehut

Maybe Github is not that bad, but regardless it's not having a vendor-lock in to Github. Additionally, it helps people who self-host to support other storage backends.

So it would be helpful if deco added support for other forges including but not limited to forgejo(codeberg), gitea, sourcehut, etc. at some point in the future.

I just created this feature request here while as in the process of slowly moving my projects to codeberg and my self-hosted forgejo instance. A lot of projects big and small are moving away from Github due to Microsoft's mismanagement and force to its co-pilot/genAI/LLM features as well as other issues. See:
https://sfconservancy.org/GiveUpGitHub/
https://ziglang.org/news/migrating-from-github-to-codeberg/
https://notgull.net/finding-a-forge/

The issue names no files, tests, or entry points. Start by locating the existing GitHub forge integration and the storage-backend boundary, then clarify the supported forge scope and authentication behavior; done means the agreed Forgejo, Gitea, or SourceHut integrations work without GitHub-specific assumptions.

Written by the indexing model from the issue text.