Support Gitea as new storage provider

[wtraylor]

It would be great to be able to add a Git repository hosted on Gitea as an Add-on of an OSF project. Gitea is under the permissive MIT license and can be self-hosted. It is a fully Free Software alternative to the all-closed-source GitHub and the partially closed-source GitLab. Therefore I consider Gitea very much in the spirit of Open Science. I think being fully open source is a prerequisite for scientific infrastructure as this is the only way to guarantee long-term availability.

GitHub and gitlab.com are both for-profit storage providers. In contrast, Gitea is used by the initiative Codeberg.org, which is a non-profit hosting service dedicated to provide a privacy-respecting and not commercially driven place for Free Software projects.