Add Sidekiq queues API to nav

Adds: https://docs.gitlab.com/ee/api/admin_sidekiq_queues.html to the global navigation. Also tier badges Sidekiq-related entries.

@smcgivern Could you just check I have the tiers right (basically, that for both the updated entries, they are unavailable on GitLab.com)?

If they look ok, could you send over to @rdickenson for merge?

Thanks!