AO3-7485 Disable user 2FA when a backup code is used

[EchoEkhi]

Pull Request Checklist

• Have you read "How to write the perfect pull request"?
• Have you read the contributing guidelines?
• Have you added tests for any changed functionality?
• Have you added the Jira issue number
  as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
• Do you have fewer than 5 pull requests already open? If not, please wait
  until they are reviewed and merged before creating new pull requests.
• Blocked by AO3-7442

Issue

https://otwarchive.atlassian.net/browse/AO3-7485

Testing Instructions

1. Turn on 2FA by going through the set-up process
2. Log out, and log back in with your password and 6-digit code
3. Observe that 2FA is still enabled
4. Log out, and log back in with your backup code
5. Observe a message saying "Successfully logged in with your backup code. Two-step verification has been disabled. [...]"
6. Observe that you have been redirected to your preferences page
7. Observe that your 2FA has been disabled
8. Log out, and log back in
9. Observe that you did not need to provide 2FA details to log back in

References

https://otwarchive.atlassian.net/browse/AO3-7442?focusedCommentId=382256

Credit

EchoEkhi (He/Him)

[brianjaustin]

Closing per https://otwarchive.atlassian.net/browse/AO3-7485?focusedCommentId=383762