This stage does the following:
- Includes a data migration to copy the values from old to new field.
- Changes business logic to switch to using new field.
- Deletes all code references of the old field.
This reverts commit 84de6bc6de
which reverts commit cebeab4348
which implements the first stage of the `values` column rename in
SiteConfiguration. However, I included a small change:
This time, we set a default value on the new `site_values` column so
that the ORM will happily deserialize the JSONField without throwing a
JSONDecodeError.
