Introduce support for validating positions in the new OffsetsRequestManager. This task will include a new event for the validatePositions calls performed from the new consumer, and the logic for handling such events in the OffsetRequestManager.
The validate positions implementation will keep the same behaviour as the one in the old consumer, but adapted to the new threading model. So it is based in a VALIDATE_POSITIONS events that is submitted to the background thread, and the processed by the ApplicationEventProcessor. The processing itself is done by the OffsetRequestManager given that this will require an OFFSET_FOR_LEADER_EPOCH request. This task will introduce support for such requests in the OffsetRequestManager, responsible for offset-related requests.