[skip ci]Add rmq consumer impl topic comment (#11533)

Signed-off-by: fishpenguin <kun.yu@zilliz.com>

internal/util/rocksmq/client/rocksmq/consumer_impl.go

@@ -90,6 +90,7 @@ func (c *consumer) Subscription() string {
 	return c.consumerName
 }
 
+// Topic returns the topic of the consumer
 func (c *consumer) Topic() string {
 	return c.topic
 }