Add logger webhook metrics in metrics-v3 (#19515)

endpoint: /minio/metrics/v3/cluster/webhook
metrics:
- failed_messages (counter)
- online (gauge)
- queue_length (gauge)
- total_messages (counter)

cmd/metrics-v2.go

@@ -295,10 +295,7 @@ const (
 	kmsRequestsFail    = "request_failure"
 	kmsUptime          = "uptime"
 
-	webhookOnline         = "online"
-	webhookQueueLength    = "queue_length"
-	webhookTotalMessages  = "total_messages"
-	webhookFailedMessages = "failed_messages"
+	webhookOnline = "online"
 )
 
 const (