v.21.9Bug Fix

Fix Limitations with Distributed Group By Settings in ClickHouse

Fix distributed_group_by_no_merge = 2 with distributed_push_down_limit = 1 or optimize_distributed_group_by_sharding_key = 1 with LIMIT BY and LIMIT OFFSET. #27249 (Azat Khuzhin). These are obscure combination of settings that no one is using.