Various improvements in replication (#11949)

- collect real time replication metrics for prometheus.
- add pending_count, failed_count metric for total pending/failed replication operations.

- add API to get replication metrics

- add MRF worker to handle spill-over replication operations

- multiple issues found with replication
- fixes an issue when client sends a bucket
 name with `/` at the end from SetRemoteTarget
 API call make sure to trim the bucket name to 
 avoid any extra `/`.

- hold write locks in GetObjectNInfo during replication
  to ensure that object version stack is not overwritten
  while reading the content.

- add additional protection during WriteMetadata() to
  ensure that we always write a valid FileInfo{} and avoid
  ever writing empty FileInfo{} to the lowest layers.

Co-authored-by: Poorna Krishnamoorthy <poorna@minio.io>
Co-authored-by: Harshavardhana <harsha@minio.io>

cmd/data-update-tracker.go

@@ -31,11 +31,9 @@ import (
 	"sync"
 	"time"
 
-	"github.com/minio/minio/cmd/config"
 	"github.com/minio/minio/cmd/logger"
 	"github.com/minio/minio/pkg/color"
 	"github.com/minio/minio/pkg/console"
-	"github.com/minio/minio/pkg/env"
 	"github.com/willf/bloom"
 )
 
@@ -80,7 +78,7 @@ func newDataUpdateTracker() *dataUpdateTracker {
 		Current: dataUpdateFilter{
 			idx: 1,
 		},
-		debug:      env.Get(envDataUsageScannerDebug, config.EnableOff) == config.EnableOn || serverDebugLog,
+		debug:      serverDebugLog,
 		input:      make(chan string, dataUpdateTrackerQueueSize),
 		save:       make(chan struct{}, 1),
 		saveExited: make(chan struct{}),