Add script+Dockerfile to test restoring from fresh backup every 24 hours

[nikochiko]

Adds Dockerfile to attempt restoring a database from the same backup (every 24 hours).

To know whether the backup succeeded, we can look at the logs. But we obviously need some kind of alerts otherwise.

We could also connect a staging / test server to this with all the prod data but without affecting prod. Setting up alerts for that server would also be good enough for us.

terrible commit messages... pls squash