Added rd_kafka_list_groups API to get consumer group subscription metadata

[simnotes]

I added new GetConsumerGroupsMetadata function to consumer, producer and adminClient API, which calls rd_kafka_list_groups from librdkafka to retrieve current consumer group status and consumer group subscriptions from broker. Via the new API it is possible to query subscription-status like in "kafka-consumer-groups.sh"

Also added integration and dry-tests to everything.

(somehow this is a copy form pr #331 )

[ghost]

@confluentinc It looks like @simnotes just signed our Contributor License Agreement. :+1:

Always at your service,

clabot

[simnotes]

@edenhill I published the included changes prior to the 1.0.0 release and you told me, that those changes might be merged after the release (which is understandable). So now I merged the 1.0.0 release with my changes, fixed the merge issues, ran the tests again and everything seems to be ok -> Do you mind, having a look again?

[nsagnett]

Hi !

Any news on this topic ? It should be a great feature !

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[milindl]

Closing this now that rd_kafka_list_groups is deprecated and replaced with rd_kafka_ListConsumerGroups and rd_kafka_DescribeConsumerGroups.

Both are available in the go client via #923.