Context

first leg of epic described in #40 (closed).

Behavior

every night run a cron job runs that:
- makes a copy of the signal_data volume and pg_dumps the db
- writes encrypted versions of both to the filesystem (encrypted to 2 maintainer keys)
- scps those files to a backup server
- destroys old backups on the backup server
the script itself lives in bin/backup
the crontab that runs the script lives in ansible/files/crontab/root
the script relies on tooling that is provisioned autmatically by ansible. see:
- ssh config files and pub/private keys need to scp backups to target are in /ansible/files/.ssh/root
- provision steps for prod (including loading crontab and creating sb_deploy user that scp's files to backup target) are in the prod_user-tagged tasks in ansible/playbooks/provision.yml
- provision steps for backup target are in ansible/playbooks/provision_backup.yml