recognize gitlab URLs

sometimes it's easier to copy-paste a gitlab URL than the magic reference in chat. it would be nice if this:

https://gitlab.torproject.org/tpo/tpa/team/-/issues/40000

would work like this:

16:49:25 <@anarcat> tpa/team#40000
16:49:25 -tor:#tor-admin- https://gitlab.torproject.org/tpo/tpa/team/-/issues/40000 - Gitlab Migration Milestone