re-use the same local drive used by remote-peer (#18645)

historically, we have always kept storage-rest-server
and a local storage API separate without much trouble,
since they both can independently operate due to no
special state() between them.

however, over some time, we have added state()
such as

- drive monitoring threads now there will be "2" of
  them per drive instead of just 1.

- concurrent tokens available per drive are now twice
  instead of just single shared, allowing unexpectedly
  high amount of I/O to go through.

- applying serialization by using walkMutexes can now
  be adequately honored for both remote callers and local
  callers.

cmd/metrics-resource.go

@@ -252,10 +252,10 @@ func collectDriveMetrics(m madmin.RealtimeMetrics) {
 	}
 
 	globalLocalDrivesMu.RLock()
-	gld := globalLocalDrives
+	localDrives := globalLocalDrives
 	globalLocalDrivesMu.RUnlock()
 
-	for _, d := range gld {
+	for _, d := range localDrives {
 		labels := map[string]string{"drive": d.Endpoint().RawPath}
 		di, err := d.DiskInfo(GlobalContext, false)
 		if err == nil {