Enable use database as truth in dev

[SamJamCul]

What problem does this pull request solve?

Trello card: https://trello.com/c/dGcFbmNo/2412-test-usedatabaseastruth-for-forms-admin-in-dev

Turns on the use_database_as_truth flag, must go in after #1671 though

Things to consider when reviewing

• Ensure that you consider the wider context.
• Does it work when run on your machine?
• Is it clear what the code is doing?
• Do the commit messages explain why the changes were made?
• Are there all the unit tests needed?
• Has all relevant documentation been updated?

Reminders

If you've made changes to the deployer role (files in modules/deployer-access):

• Remember to run make <environment> forms/account apply on the relevant environments (dev, staging, user-research, and/or prod)
• Check the #govuk-forms-deployment-notifications Slack channel to ensure the apply-forms-terraform-<environment> pipelines have run successfully