This series moves the logic to not perform off-strategy compaction if the maintenance set is empty from the table layer down to the compaction_manager layer since it is the one that needs to make the decision.
With that compaction_manager::perform_offstrategy will return a future<bool> which resolves to true
iff off-strategy compaction was required and performed.
The sstable_compaction_test was adjusted and a new compaction_manager_for_testing class was added
to make sure the compaction manager is enabled when constructed (it wasn't so test_offstrategy_sstable_compaction didn't perform any off-strategy compactions!) and stopped before destroyed.
Closes#10848
* github.com:scylladb/scylla:
table: perform_offstrategy_compaction: move off-strategy logic to compaction_manager
compaction_manager: offstrategy_compaction_task: refactor log printouts
test: sstable_compaction: compaction_manager_for_testing
1f4f8ba773