@hugopeixoto, ForgeFed is going through tech stack changes, so the spec is unstable, but all of us here will be working together in coordination. I can happily give you an overview of the technology and you’d have plenty of work to do in GitLab 
essentially same work that is being done in parallel in Gitea/Forgejo and in Vervis; and GitLab joining in would be great! Vervis and Gitea/Forgejo are already a few steps ahead so you should be able to test your code against them.