Add additional info for replication metrics API (#17293)

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

cmd/xl-storage.go

@@ -619,6 +619,7 @@ func (s *xlStorage) NSScanner(ctx context.Context, cache dataUsageCache, updates
 			}
 			for tgt, st := range sizeS.replTargetStats {
 				res["repl-size-"+tgt] = strconv.FormatInt(st.replicatedSize, 10)
+				res["repl-count-"+tgt] = strconv.FormatInt(st.replicatedCount, 10)
 				if st.failedCount > 0 {
 					res["repl-failed-"+tgt] = fmt.Sprintf("%d versions, %d bytes", st.failedCount, st.failedSize)
 				}