hints: propagate abort signal correctly in wait_for_sync_point
hints: propagate abort signal correctly in wait_for_sync_point

When `manager::wait_for_sync_point` is called, the abort source from the
arguments (`as`) might have already been triggered. In such case, the
subscription which was supposed to trigger the `local_as` abort source
won't be run, and the code will wait indefinitely for hints to be
replayed instead of checking the replay status and returning
immediately.

This commit fixes the problem by manually triggering `local_as` if `as`
have been triggered.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla