Add system CPU metrics to metrics-v3 (#19560)

endpoint: /minio/metrics/v3/system/cpu

metrics:
- minio_system_cpu_avg_idle
- minio_system_cpu_avg_iowait
- minio_system_cpu_load
- minio_system_cpu_load_perc
- minio_system_cpu_nice
- minio_system_cpu_steal
- minio_system_cpu_system
- minio_system_cpu_user

cmd/metrics-v3-cache.go

@@ -35,6 +35,7 @@ type metricsCache struct {
 	esetHealthResult    *cachevalue.Cache[HealthResult]
 	driveMetrics        *cachevalue.Cache[storageMetrics]
 	memoryMetrics       *cachevalue.Cache[madmin.MemInfo]
+	cpuMetrics          *cachevalue.Cache[madmin.CPUMetrics]
 	clusterDriveMetrics *cachevalue.Cache[storageMetrics]
 	nodesUpDown         *cachevalue.Cache[nodesOnline]
 }
@@ -45,6 +46,7 @@ func newMetricsCache() *metricsCache {
 		esetHealthResult:    newESetHealthResultCache(),
 		driveMetrics:        newDriveMetricsCache(),
 		memoryMetrics:       newMemoryMetricsCache(),
+		cpuMetrics:          newCPUMetricsCache(),
 		clusterDriveMetrics: newClusterStorageInfoCache(),
 		nodesUpDown:         newNodesUpDownCache(),
 	}
@@ -200,6 +202,31 @@ func newDriveMetricsCache() *cachevalue.Cache[storageMetrics] {
 		loadDriveMetrics)
 }
 
+func newCPUMetricsCache() *cachevalue.Cache[madmin.CPUMetrics] {
+	loadCPUMetrics := func() (v madmin.CPUMetrics, err error) {
+		var types madmin.MetricType = madmin.MetricsCPU
+
+		m := collectLocalMetrics(types, collectMetricsOpts{
+			hosts: map[string]struct{}{
+				globalLocalNodeName: {},
+			},
+		})
+
+		for _, hm := range m.ByHost {
+			if hm.CPU != nil {
+				v = *hm.CPU
+				break
+			}
+		}
+
+		return
+	}
+
+	return cachevalue.NewFromFunc(1*time.Minute,
+		cachevalue.Opts{ReturnLastGood: true},
+		loadCPUMetrics)
+}
+
 func newMemoryMetricsCache() *cachevalue.Cache[madmin.MemInfo] {
 	loadMemoryMetrics := func() (v madmin.MemInfo, err error) {
 		var types madmin.MetricType = madmin.MetricsMem