Migrate previously existing user accounts to new passwordless system

I noticed my previous data was not accessible through my newer account, and I don't think we ever migrated existing accounts?

We would need to:

- Iterate over all accounts with an email
- Generate a hash using the new algorithm
- If new account with that hash exists, find all responses for old account and assign them the new `userId` for the new account
- If no new account exists, recalculate hash using new algorithm and delete email (since we don't want to store them).