Move GitLab UI Rails form builder into its own project/gem

In !64260 (merged) we added a custom rails form builder for GitLab UI fields. There was some discussion around moving this into its own project and using CI to publish a Ruby gem that can be consumed by gitlab-org/gitlab.

Two options are:

  1. Create a new project
  2. Add to the gitlab-org/gitlab-ui project
Edited by Peter Hegman