Support show-all-refs for git over HTTP

What does this MR do?

Library code allowing the ShowAllRefs parameter to be set for git-http requests (handled by workhorse).

Are there points in the code the reviewer needs to double check?

Nothing in CE uses this library code yet. EE will require it for Geo clone over HTTPS support, but it may be useful for backups, exports, etc, in CE. Since the Workhorse code is MIT, there's no value in having this be EE-only.

This will need an updated GITLAB_WORKHORSE_VERSION. It is WIP until that's released.

Why was this MR needed?

Prerequisite of Geo sync over HTTPS support

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/3341 gitlab-workhorse#149 (closed)