Depends on: https://github.com/alphagov/notifications-api/pull/3314
Previously:
- We introduced a new "areas_2" API field that's can
populate the "areas" column in the same way.
- We updated the Admin app to use the new field, so that
the old "areas" and "simple_polygons" API fields are unused.
- We repurposed the unused "areas" API field to use
the new "areas_2" format.
This PR:
- We can switch the Admin app back to the "areas" field,
but in the new format.
Future PRs:
- Remove support for the unused "areas_2" field (migration complete)