Add support for gitlab: ...

[sol]

Add a gitlab: ... analog to github: ....

Example packages that could benefit from this:

• https://gitlab.com/paolo.veronelli/hasql-pipes
• https://gitlab.com/morley-framework/indigo
• https://gitlab.com/devs.global.de/tasty-bdd

(more: https://www.google.com/search?q=site%3Ahackage.haskell.org+intext%3Agitlab+-gitlab-haskell+-gitlab-api+-vcs-web-hook-parse+-gli+-yesod-auth-oauth2&oq=site%3Ahackage.haskell.org+intext%3Agitlab+-gitlab-haskell+-gitlab-api+-vcs-web-hook-parse+-gli+-yesod-auth-oauth2)

Request before by @dpwiz (#79).

[mgajda]

Since I moved to GitLab from GitHub, all my packages would benefit too: https://gitlab.com/migamake

[dpwiz]

I were frustrated once again with github plastered everywhere and tried to add a gitlab field... Then I remembered there are more services and projects like gitea make those even more desirable.

Good news: There's even a common schema https://<service>/<owner>/<repo>[/subdirs...]
Bad news: "owner" can also be a nested subgroup path inside a project group. That's gonna clash with #444.

Anyway, simply recognizing gitlab: field can do some good with minimal maintenance.
Perhaps a unified type based upon Hpack.Config.GitHub may serve the purpose. It can be extended with the "well-known" field that'll provide the URL template.

And a way to extend support toward self-hosted repos may be devised next.

[dpwiz]

There is a vcs/forge discovery protocol in the works talks, originating from godocs.io:

https://lists.sr.ht/~ancarda/vcs-autodiscovery/%3CCFA7DXTFDWXD.1YR4U9KQT6YJ0%40nitro%3E