This task is to thread-through the creation and cleanup of the CollectionRangeDeleter object. A single instance must exist at any given time, if and only if there are entries in the MetadataManager::_rangesToClean object and it should be created the first time an entry is put in there.

You'll need to implement the following:

    CollectionRangeDeleter::run() {
        if (cleanupNext())
            (range deleter task executor).scheduleTask()
        else
            delete this
    }

And in MetadataManager, you'll need to create the CollectionRangeDeleter and schedule the task in MetadataManager::addToRTC, which should do so if the rangesToClean was previously empty. The CollectionRangeDeleter should be created on the heap, and then CollectionRangeDeleter::run() will handle deleting it when it is finished.

Once that is implemented, we'll need to figure out how to clean up the CollectionRangeDeleter object when the server crashes/shutsdown/something bad happens to the scheduled task on the task executor.

This also involves writing unit-tests.