Skip `authenticate_user!` for Doorkeeper controllers

What does this MR do?

This just adds the required methods to the Doorkeeper::ApplicationController by adding a new Gitlab::DoorkeeperBaseController instead of having ApplicationController and having to deal with authentication.

We needed to make sure FastGettext is initialized before any controllers, so I moved that initializer to avoid errors like:

/Users/bvl/.rbenv/versions/2.3.7/lib/ruby/gems/2.3.0/gems/fast_gettext-1.6.0/lib/fast_gettext/storage.rb:79:in `current_repository': Current textdomain (nil) was not added, use FastGettext.add_text_domain ! (FastGettext::Storage::NoTextDomainConfigured)

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 UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/44639