build: dbmigrate docker image

[favna]

This needs testing but I just wanted to braindump my current thoughts on GitHub.

The way to configure this is to pass the environment variable DATABASE_URL through the -e flag for docker run or the docker compose file. Setting it to something like

DATABASE_URL=postgresql://postgres:postgres@postgres:5432/teryl?schema=public

wherein postgres@5432 targets the containerized postgres so it goes docker-to-docker