Do not list or describe non-consumer groups

[mborst]

When listing or describing groups via a ListGroups or DescribeGroups request, Kafka also returns non-consumer groups, e.g. Kafka Connect groups. Those should be omitted when listing or describing consumer groups, just as in the official implementation [1].

[1] https://github.com/apache/kafka/blob/13ffebe2f1012da473189c4fe86fd14b83809962/clients/src/main/java/org/apache/kafka/clients/admin/KafkaAdminClient.java#L3428

---

This change is 

[jeffwidman]

The idea makes sense, I haven't had time to look through the implementation, but I'm 👍 on the idea. The one thing I vaguely remember is there are consumer groups from kafka < 0.9(??) that don't have their protocol type mentioned, so they need to be included here along with the explicit consumer group type. I may be mis-remembering though, it's been a few years since I worked on this.

[mborst]

Wouldn't that be covered by this, and in the same way as in the reference implementation?

[mborst]

Is there anything I can do to get this merged?