[skip e2e] Add comment for getDqlChannelsFunc (#13783)

Signed-off-by: Ndragondriver <jiquan.long@zilliz.com>

internal/proxy/channels_mgr.go

@@ -103,6 +103,7 @@ func getDmlChannelsFunc(ctx context.Context, rc types.RootCoord) getChannelsFunc
 	}
 }
 
+// getDqlChannelsFunc returns a function about how to get query channels of a collection.
 func getDqlChannelsFunc(ctx context.Context, proxyID int64, qc createQueryChannelInterface) getChannelsFuncType {
 	return func(collectionID UniqueID) (map[vChan]pChan, error) {
 		req := &querypb.CreateQueryChannelRequest{