Add an automated database backup

[j2kun]

See https://docs.docker.com/storage/volumes/#backup-a-container

[j2kun]

Also see: https://www.postgresql.org/docs/9.1/backup-dump.html

pg_dump dbname | gzip > filename.gz
Reload with:

gunzip -c filename.gz | psql dbname
or:

cat filename.gz | gunzip | psql dbname