Not even that is necessary.
> The best solution probably is to create a new database during image creation, but in the official Postgres image this option is still not available.
The official image's README (https://registry.hub.docker.com/_/postgres/) says otherwise - both a user and a database will be created with name $POSTGRES_USER (if set).
Furthermore, one can run postgres in single-user mode to prepare any initial db image on top of the official one.
well ideally you would have a script to create the DB and possibly migrate it. IE this will create a PG database from `DATABASE_URL`
then it's simply a matter of `fig up` + `fig run web python manage.py createdb`