[skip ci]Add comment for GetMetrics (#11198)

Signed-off-by: Nsunby <bingyi.sun@zilliz.com>

internal/distributed/datacoord/client/client.go

@@ -511,6 +511,7 @@ func (c *Client) GetFlushedSegments(ctx context.Context, req *datapb.GetFlushedS
 	return ret.(*datapb.GetFlushedSegmentsResponse), err
 }
 
+// GetMetrics gets all metrics of datacoord
 func (c *Client) GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error) {
 	ret, err := c.recall(func() (interface{}, error) {
 		client, err := c.getGrpcClient()