`Gitea` support

[Kaiser-Yang]

Add Gitea support.

Add an doc for how to add new support for different git centers using Gitea as an example.

[choucavalier]

agreed, could be useful for Codeberg users for example

[Kaiser-Yang]

I've written documentation, but I have no time to add support for gitea.

https://github.com/Kaiser-Yang/blink-cmp-git?tab=readme-ov-file#how-to-add-new-git-platforms

PRs are welcome.