DDLs issued immediately after a rebalance fail with Operation cannot be performed during rebalance

With the improvement in rebalance time perception by reporting rebalances as complete before resuming ingestion, there is a window in which received DDLs will report as Operation cannot be performed during rebalance during the resume. A better experience would be to to block DDLs (like we do DMLs) when performing post-rebalance activities while holding the rebalance lock.