Acceptance Testing: Rate Limiter

~Conversation: #429 (closed)

Blocked On: omnibus-gitlab#2839 (closed)

We need to test rate limiting in dev and staging before enabling it in production through config changes.

Testing approach:

1. Come up with an approach to configuring rate limits in production environments: #429 (comment 41899474)
2. Test on dev and staging
3. On a single server, for a few problem RPCs, add a very high limit and monitor with the new metrics that were added as part of this change.
4. Bring the metrics down to a reasonable level, once we have an idea of what reasonable is.
5. Rinse, repeat.
6. Once we're happy with the limits, roll them out across the file server fleet.

cc @pcarranza @eReGeBe @ahmadsherif wdyt?