Support KIP-345 / Static Consumer Group Membership

[DenisKuplyakov]

The only question is in subj. I've googled and searched this repo, no clues. Have seen only a merge-request to support Incremental Cooperative Rebalancing Static Consumer Group Membership.

KIP-345: https://cwiki.apache.org/confluence/display/KAFKA/KIP-345%3A+Introduce+static+membership+protocol+to+reduce+consumer+rebalances

(Note: Incremental Cooperative Rebalancing is via KIP-429 and tracked in #2143)

[jeffwidman]

No one has submitted support for it yet, but we would certainly welcome a PR!