Summary:
This PR adds a missing piece for the UDT in memtable only feature, which is to automatically increase `full_history_ts_low` when flush happens during recovery.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11774

Test Plan:
Added unit test
make all check

Reviewed By: ltamasi

Differential Revision: D48799109

Pulled By: jowlyzhang

fbshipit-source-id: fd681ed66d9d40904ca2c919b2618eb692686035