[APER-3241]
This PR updates the retirement pipeline to purge learners' names from certificate records when their account is being retired.
It also introduces a new management command that can be used by Open edX operators to purge the leftover name data (PII data) from the `certificates_generatedcertificate` table. This is designed as a one-time use data fixup, as the retirement functionality should clean this moving forward.