* refactor: make compactor_scheduler crate
* refactor: move PartitionsSource into the compactor_scheduler
The compactor currently uses PartitionsSource in two ways:
* for the preparation of PartitionIds prior to the compactor pipeline.
* for the abstraction which utilize the PartitionIds during the IO pipeline.
This commit is a refactoring to enable us to delineate between these two utilizations.
The former (preparation) utilization will now be done in the compactor_scheduler.
Since the compactor is dependent on the compactor_scheduler, it made sense to move the trait to the scheduler.
wiedld