This stage does the following:
- Adds the new field and migration to create the column.
- Makes all* writes go to both old and new field.
(*) Except for writes from the Django Admin for this model. I confirmed
with Support that CreditRequirements are never edited through the Django
Admin interface. Additionally, I confirmed via the django_admin_log
that there is no record of anybody changing any CreditRequirements.
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