New `gitlab:workhorse:install` rake task

What does this MR do?

This adds a new gitlab:workhorse:install Rake task similar to the gitlab:shell:install task.

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

• Do we need the check for gmake? I've added it since the documentation mentioned that "If you are not using Linux you may have to run gmake instead of make below"...
• The specs are little complex, but at least it is testing the task so I think it's useful! I'm open to suggestion on how to improve them, though.
• Do I need to update any other files regarding the new gitlab_workhorse.path option?

Why was this MR needed?

Because with this we can remove the "Ensure the gitlab-workhorse version in Install gitlab-workhorse matches the required version." step from https://gitlab.com/gitlab-org/release-tools/blob/master/doc/release-candidates.md#creating-rc1! MR is ready: release-tools!57 (merged)

Closes #22719 (closed)