Is your feature request related to a problem? Please describe.
The ReIndex task deletes all documents from the index, leaving it empty until the IndexQueueWorker has processed the queue. It removes only documents from the types, scheduled to be indexed, leaving files in the index forever.

Describe the solution you'd like
A proper cleanup task, that accepts a time threshold to delete old documents, leaving the newer ones in the index.

Target versions
The newest release, but it may also be backported to 11.x, as this could really be helpful.