Add support for self-hosted GitLab instances for Git permalinks (#19909)

This PR adds support for self-hosted GitLab instances when generating
Git permalinks.

If the `origin` Git remote contains `gitlab` in the URL hostname we will
then attempt to register it as a self-hosted GitLab instance.

A note on this: I don't think relying on specific keywords is going to
be a suitable long-term solution to detection. In reality the
self-hosted instance could be hosted anywhere (e.g.,
`vcs.my-company.com`), so we will ultimately need a way to have the user
indicate which Git provider they are using (perhaps via a setting).

Closes https://github.com/zed-industries/zed/issues/18012.

Release Notes:

- Added support for self-hosted GitLab instances when generating Git
permalinks.
- The instance URL must have `gitlab` somewhere in the host in order to
be recognized.