Add cluster audit metrics in metrics-v3 (#19514)

endpoint: /minio/metrics/v3/cluster/audit
metrics:
- failed_messages (counter)
- total_messages (counter)
- target_queue_length (gauge)

cmd/metrics-v3.go

@@ -43,6 +43,7 @@ const (
 	clusterUsageObjectsCollectorPath collectorPath = "/cluster/usage/objects"
 	clusterUsageBucketsCollectorPath collectorPath = "/cluster/usage/buckets"
 	clusterErasureSetCollectorPath   collectorPath = "/cluster/erasure-set"
+	clusterAuditCollectorPath        collectorPath = "/cluster/audit"
 )
 
 const (
@@ -218,6 +219,15 @@ func newMetricGroups(r *prometheus.Registry) *metricsV3Collection {
 		loadClusterErasureSetMetrics,
 	)
 
+	clusterAuditMG := NewMetricsGroup(clusterAuditCollectorPath,
+		[]MetricDescriptor{
+			auditFailedMessagesMD,
+			auditTargetQueueLengthMD,
+			auditTotalMessagesMD,
+		},
+		loadClusterAuditMetrics,
+	)
+
 	allMetricGroups := []*MetricsGroup{
 		apiRequestsMG,
 		apiBucketMG,
@@ -230,6 +240,7 @@ func newMetricGroups(r *prometheus.Registry) *metricsV3Collection {
 		clusterUsageObjectsMG,
 		clusterUsageBucketsMG,
 		clusterErasureSetMG,
+		clusterAuditMG,
 	}
 
 	// Bucket metrics are special, they always include the bucket label. These