[skip ci]Add comment for datacoord client (#9752)

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

internal/distributed/datacoord/client/client.go

@@ -46,6 +46,7 @@ type Base interface {
 	Register() error
 }
 
+// Client is the datacoord grpc client
 type Client struct {
 	ctx    context.Context
 	cancel context.CancelFunc