[APER-3385]
This PR fixes an existing management command that now has incorrect logic. We have recently done a lot of work to
improve certificate-related date business logic to fix data inconsistencies between systems. Instead of maintaining
separate and duplicated logic for sending date data to Credentials, instead we can use an existing (and tested)
Celery task that will determine and send the correct date to the Credentials IDA.
Additionally, the original version of this management command skipped self-paced courses completely. This is no
longer the case as we _know_ that there are self-paced courses that have been associated with a certificate available
date because of bugs in the product. This management command will serve as a means to do a mass data fixup for data stored by the Credentials IDA.
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