Services are unfrozen before `initBackgroundReplication` is finished. This means that
the globalReplicationStats write is racy. Switch to an atomic pointer.
Provide the `ReplicationPool` with the stats, so it doesn't have to be grabbed
from the atomic pointer on every use.
All other loads and checks are nil, and calls return empty values when stats
still haven't been initialized.
to track the replication transfer rate across different nodes,
number of active workers in use and in-queue stats to get
an idea of the current workload.
This PR also adds replication metrics to the site replication
status API. For site replication, prometheus metrics are
no longer at the bucket level - but at the cluster level.
Add prometheus metric to track credential errors since uptime
