[skip ci] Add graceful stop grpc server log in datanode (#12923)

Signed-off-by: yun.zhang <yun.zhang@zilliz.com>

Co-authored-by: yun.zhang <yun.zhang@zilliz.com>

internal/distributed/datanode/service.go

@@ -159,6 +159,7 @@ func (s *Server) Stop() error {
 	}
 	s.cancel()
 	if s.grpcServer != nil {
+		log.Debug("Graceful stop grpc server...")
 		// make graceful stop has a timeout
 		stopped := make(chan struct{})
 		go func() {