[jetstream] Fix setting omitted QueueGroupName on ConsumerConfig (#2835)

Signed-off-by: Byron Ruth <byron@nats.io>

pubsub/jetstream/jetstream.go

@@ -153,6 +153,9 @@ func (js *jetstreamPubSub) Subscribe(ctx context.Context, req pubsub.SubscribeRe
 	if v := js.meta.DurableName; v != "" {
 		consumerConfig.Durable = v
 	}
+	if v := js.meta.QueueGroupName; v != "" {
+		consumerConfig.DeliverGroup = v
+	}
 
 	if v := js.meta.internalStartTime; !v.IsZero() {
 		consumerConfig.OptStartTime = &v