Checklist

• I've searched the issue queue to verify this is not a duplicate feature request.
• I've pasted the output of kargo version, if applicable.
• I've pasted logs, if applicable.

Proposed Feature

Add native Gitea integration for the following steps in Kargo:

git-open-pr: Support creating pull requests for repositories hosted on Gitea.
git-wait-for-pr: Support waiting for pull requests to be approved and merged within Gitea.

Motivation

Gitea is a great alternative to selfhost a git registry. Also Gitea has a great and important open source community.

Suggested Implementation

Add the gitea git provider inside internal/gitprovider folder, using their SDK.

Notes

I opened a pull request here