this parameter defaults to do_flush::yes, so the existing behavior is
preserved. and this change prepares for a change which flushes all
tables before performing cleanup on the tables per-demand.
please note, we cannot pass compaction::flush_mode to this function,
as it is used by compaction/task_manager_module.hh, if we want to
share it by both database.hh and compaction/task_manager_module.hh,
we would have to find it a new home. so `table::do_flush` boolean
tag is reused instead.
Refs #16757
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>