Add list_consumer_group_offsets()

Support fetching the offsets of a consumer group.

Note: As far as I can tell (the Java code is a little inscrutable), the
Java AdminClient doesn't allow specifying the `coordinator_id` or the
`partitions`.

But I decided to include them because they provide a lot of additional
flexibility:

1. allowing users to specify the partitions allows this method to be used even for
older brokers that don't support the OffsetFetchRequest_v2

2. allowing users to specify the coordinator ID gives them a way to
bypass a network round trip. This method will frequently be used for
monitoring, and if you've got 1,000 consumer groups that are being
monitored once a minute, that's ~1.5M requests a day that are
unnecessarily duplicated as the coordinator doesn't change unless
there's an error.

0 files changed, 0 insertions, 0 deletions