Commits to retained partitions should continue during cooperative rebalance

[bplommer]

Currently we don't perform any commits during a rebalance - this is correct for the greedy rebalance protocol, but for the cooperative protocol where not all partitions are revoked at the beginning we should (I think?) keep committing to retained partitions.

[okouyad]

@bplommer does that mean that fs2-kafka does not support the CooperativeStickyAssignor ? at this point ?

[okouyad]

I mean i just made a search for this because i have set it in my code and experienced some weird behavior, then decided to see if there were issue with it. Hence seeing this i am wondering what is the consequence of this open issue ? how not haaving this functionality set up impact the behavior of fs2-kafka