Check auth before limit handler

With V2 Auth, the timestamp the token was created at matters. In the situation where the limit handler queues requests for more than 30 seconds, when the requests go forward they will fail auth because their tokens will be expired.

Instead, if we check auth before the limit handler queues the requests, this will not happen.

This is what was causing ReplicateRepository to break in production for www-gitlab-com, because it takes a long time for that repository to replicate, and we were setting the concurrency limit for ReplicateRepository to 1. This was causing subsequent calls to fail auth.

fixes: #2815 (closed)