Compaction tasks which do not have a parent are abortable
through task manager. Their children are aborted recursively.
Compaction tasks of the lowest level are aborted using existing
compaction task executors stopping mechanism.
Closesscylladb/scylladb#16050
* github.com:scylladb/scylladb:
test: test abort of compaction task that isn't started yet
test: test running compaction task abort
tasks: fail if a task was aborted
compaction: abort task manager compaction tasks