Add support for resource metrics (#18057)

Add a new endpoint for "resource" metrics `/v2/metrics/resource`

This should return system metrics related to drives, network, CPU and
memory. Except for drives, other metrics should have corresponding "avg"
and "max" values also.

Reuse the real-time feature to capture the required data,
introducing CPU and memory metrics in it.

Collect the data every minute and keep updating the average and max values
accordingly, returning the latest values when the API is called.

cmd/peer-rest-client.go

@@ -229,6 +229,33 @@ func (client *peerRESTClient) GetMetrics(ctx context.Context, t madmin.MetricTyp
 	return info, err
 }
 
+func (client *peerRESTClient) GetResourceMetrics(ctx context.Context) (<-chan Metric, error) {
+	respBody, err := client.callWithContext(ctx, peerRESTMethodResourceMetrics, nil, nil, -1)
+	if err != nil {
+		return nil, err
+	}
+	dec := gob.NewDecoder(respBody)
+	ch := make(chan Metric)
+	go func(ch chan<- Metric) {
+		defer func() {
+			xhttp.DrainBody(respBody)
+			close(ch)
+		}()
+		for {
+			var metric Metric
+			if err := dec.Decode(&metric); err != nil {
+				return
+			}
+			select {
+			case <-ctx.Done():
+				return
+			case ch <- metric:
+			}
+		}
+	}(ch)
+	return ch, nil
+}
+
 // GetProcInfo - fetch MinIO process information for a remote node.
 func (client *peerRESTClient) GetProcInfo(ctx context.Context) (info madmin.ProcInfo, err error) {
 	respBody, err := client.callWithContext(ctx, peerRESTMethodProcInfo, nil, nil, -1)