[skip ci]Add comment for WatchChannels in types.go (#12415)

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

internal/types/types.go

@@ -229,6 +229,7 @@ type DataCoord interface {
 	GetCompactionState(ctx context.Context, req *milvuspb.GetCompactionStateRequest) (*milvuspb.GetCompactionStateResponse, error)
 	GetCompactionStateWithPlans(ctx context.Context, req *milvuspb.GetCompactionPlansRequest) (*milvuspb.GetCompactionPlansResponse, error)
 
+	// WatchChannels notifies DataCoord to watch vchannels of a collection
 	WatchChannels(ctx context.Context, req *datapb.WatchChannelsRequest) (*datapb.WatchChannelsResponse, error)
 	// GetFlushState gets the flush state of multiple segments
 	GetFlushState(ctx context.Context, req *milvuspb.GetFlushStateRequest) (*milvuspb.GetFlushStateResponse, error)