Thanks to @MagicRB for doing the majority of work!
The documentation still needs to be updated,
but you can already interfere parts of it from the configuration example: buildbot-nix/examples/master.nix at a36953b52d6bb9a52da2f5edce9abba18bd595c5 · Mic92/buildbot-nix · GitHub
You can see gitea + buildbot in action here: #1306 - Throw error on missing clanModule description or if description too long. Add xfce description. - clan-core - gitea: Gitea Service