* Don't bother trying to save metrics when we don't have a barrier. Use stateLock.
* Use c.barrier instead of c.systemBarrierView, thus we don't need locking
and don't need to worry about race with mount setup.
* Remove unneccessary lock.
Increment a counter whenever a request is received.
The in-memory counter is persisted to counters/requests/YYYY/MM.
When the month wraps around, we reset the in-memory counter to
zero.
Add an endpoint for querying the request counters across all time.
