[skip ci]Add comments for rocksmq producer_impl (#10695)

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

internal/util/rocksmq/client/rocksmq/producer_impl.go

@@ -57,6 +57,7 @@ func (p *producer) Send(message *ProducerMessage) (UniqueID, error) {
 	return ids[0], nil
 }
 
+// Close destroy the topic of this producer in rocksmq
 func (p *producer) Close() {
 	err := p.c.server.DestroyTopic(p.topic)
 	if err != nil {