Fix deadlock between pc-control and pc-broker-poll threads where partitions are revoked

[nachomdo]

Fixes #541

Checklist

• Documentation (if applicable)
• Changelog

[what-the-diff]

• The copyright year was changed from 2022 to 2023.
• A new method called maybeAcquireCommitLock() is added in the onPartitionsRevoked(). This will acquire a lock before committing offsets, which prevents multiple threads from accessing this function at the same time and causing race conditions.
• In PartitionState class, we have removed some unnecessary code that checks if there are any partitions assigned to it or not because now we can be sure that only one thread accesses each partition state object at a given point of time due to locks acquired by maybeAcquireCommitLock(). So no need for synchronization here anymore!
• We also remove an unused variable "partition" in ProcessingShard class as well as another check condition (if(workContainer != null)) inside WorkContainer's getWork() method since these were used when parallel consumer had more than 1 worker per topic-partition pair but now with just 1 worker per tp pair, they're redundant and cause confusion/bugs so removing them makes things simpler :)

[rkolesnev]

Please add a relevant test.
Please add changelog entry and do a local build or run process-sources to re-generate readme with updated changelog.

[rkolesnev]

LGTM