rgw/multisite: expose lock latency as perf counter for data sync

rgw/multisite: expose lock latency as perf counter for data sync

Add a "lock_latency" perf counter to the per-zone data sync counter.
This tracks the latency of RADOS lock/unlock operations in
RGWContinuousLeaseCR, giving operators visibility into the values
driving the LatencyConcurrencyControl.

The new perf counter can be queried via the admin socket:
  ceph daemon <asok> perf dump data-sync-from-<zone>
and reset independently:
  ceph daemon <asok> perf reset data-sync-from-<zone>

This would allow us to distinguish a poisoned average from ongoing
OSD latency issues without restarting the RGW process.

Signed-off-by: Oguzhan Ozmen <oozmen@bloomberg.net>