We build a custom postgres image in order to add a file to /docker-entrypoint-initdb.d/

https://github.com/metabrainz/critiquebrainz/blob/master/docker/pg_custom/Dockerfile

This can be streamlined by just mounting the sql file into the container using a volume definition in the docker-compose file. This will simplify the setup, and result in us not having to build extra images