allow gitlab repositories to be fetched

[mathildedd]

In addition to Github, Gitlab is a big player.

Let's allow to fetch metadata from there as well.

[mathildedd]

looking into this.

It is possible to do anonymous calls in gitlab's API as long as the resource is publicly available.
For example
curl https://git.drupalcode.org/api/v4/projects/19203/repository/commits returns a list of commits.

[mathildedd]

the data given by this is the same as we would get from a raw git call I believe