[12.0] Add support for prefixed URIs on base path

[abelharisov]

Support custom gitlab installations with url like host/some/path/to/gitlab

[stale]

This issue has been automatically marked as stale because there has been no recent activity. It will be closed after 30 days if no further activity occurs. Thank you for your contributions.

[GrahamCampbell]

Thanks for the PR. I feel that this is a breaking change, so I think we need to delay this until a v12.0.0 release.

[stale]

This issue has been automatically marked as stale because there has been no recent activity. It will be closed after 30 days if no further activity occurs. Thank you for your contributions.

[GrahamCampbell]

not stale

[stale]

This issue has been automatically marked as stale because there has been no recent activity. It will be closed after 30 days if no further activity occurs. Thank you for your contributions.

[GrahamCampbell]

Not stale

[GrahamCampbell]

This PR is still in consideration for the next major version.

[datawench]

Any thoughts on when this might become current? I happen to have a project that has a nonstandard self-hosted path (it's like gitlab.myproject.com/gitlab), and it's taken me a while to track down that this is why the host attribute of the request's URI gets hosed.