fetch bucket replication stats across peers in single call (#14956)

current implementation relied on recursively calling one bucket
at a time across all peers, this would be very slow and chatty
when there are 100's of buckets which would mean 100*peerCount
amount of network operations.

This PR attempts to reduce this entire call into `peerCount`
amount of network calls only. This functionality addresses also a
concern where the Prometheus metrics would significantly slow
down when one of the peers is offline.

cmd/peer-rest-common.go

@@ -18,7 +18,7 @@
 package cmd
 
 const (
-	peerRESTVersion       = "v21" // Add netperf
+	peerRESTVersion       = "v22" // Add bulk GetBucketStats
 	peerRESTVersionPrefix = SlashSeparator + peerRESTVersion
 	peerRESTPrefix        = minioReservedBucketPath + "/peer"
 	peerRESTPath          = peerRESTPrefix + peerRESTVersionPrefix
@@ -41,6 +41,7 @@ const (
 	peerRESTMethodDeleteBucketMetadata        = "/deletebucketmetadata"
 	peerRESTMethodLoadBucketMetadata          = "/loadbucketmetadata"
 	peerRESTMethodGetBucketStats              = "/getbucketstats"
+	peerRESTMethodGetAllBucketStats           = "/getallbucketstats"
 	peerRESTMethodServerUpdate                = "/serverupdate"
 	peerRESTMethodSignalService               = "/signalservice"
 	peerRESTMethodBackgroundHealStatus        = "/backgroundhealstatus"