Add rake task to migrate data from old columns in Submissions

[theseanything]

"delivery_status" is to replace "mail_status", and "last_delivery_attempt" is to replace "sent_at". To drop the old column, this adds a rake task to ensure that data in the new columns is in sync with the old columns. After this task is run, we can remove usage and drop the old columns.

[DavidBiddle]

Change looks good anyd works for me locally. The new task might benefit from some tests but I think that's optional given that it's a oneoff task we'll be deleting almost immediately.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[theseanything]

Change looks good anyd works for me locally. The new task might benefit from some tests but I think that's optional given that it's a oneoff task we'll be deleting almost immediately.

Yeah, I've manually run this and confident this runs as expected - don't think it's worth the effort for adding the tests.

[github-actions]

🎉 A review copy of this PR has been deployed! It is made of up two components

1. A review copy of forms-runner
2. A production copy of forms-admin

Important

Not all of the functionality of forms-runner is present in review apps.
Functionality such as sending emails, file upload, and S3 submission types are
deliberately disabled for the sake of simplifying review apps.

You should use the full dev environment to test the functionality which is disabled here.

It may take 5 minutes or so for the application to be fully deployed and working. If it still isn't ready
after 5 minutes, there may be something wrong with the ECS task. You will need to go to the integration AWS account
to debug, or otherwise ask an infrastructure person.

For the sign in details and more information, see the review apps wiki page.