[skip ci]Add comment for grpcdatacoordclient (#9209)

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

internal/distributed/datacoord/service.go

@@ -9,6 +9,7 @@
 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 // or implied. See the License for the specific language governing permissions and limitations under the License.
 
+// Package grpcdatacoordclient contains grpc interfaces of datacoord
 package grpcdatacoordclient
 
 import (