Support Codeberg (forgejo) repositories

**Is your feature request related to a problem? Please describe.**

I have a project hosted on https://codeberg.org/ for which I'd like to use the all-contributors CLI. However, `repoType` doesn't have an option for the Forgejo API.

**Describe the solution you'd like**

Ideally, make whatever calls are needed through the [Forgejo API](https://codeberg.org/api/swagger#/user). Failing that, there could be a `repoType=none` value to tell the CLI to ask for the profile link and avatar URL directly, instead of calling any API.

**Describe alternatives you've considered**

It's still possible to add people using their Github usernames, followed by manual fixup to point at Codeberg profiles, but it's not ideal.