Notification storage change in PR #737

[Jason Owen]

Hi everyone,

I just merged PR #737, which causes the PSM to store sent email notifications in the database. If you deploy a new version of the PSM, you will encounter errors in creating new users and in modifying enrollments until you take some action.

- If you're comfortable using psql, you can use the instructions in the pull request to update your database.
- Or, you can recreate your database and use the updated seed.sql file, which contains the definition of the new table.

This change allows the PSM to keep track of what notifications it has sent to providers, which is useful both for auditing purposes and as a first step towards allowing a state reviewer to see what emails the PSM has sent to a provider.

Thanks,
Jason