See https://team.picasoft.net/picasoft/pl/drrryr5pjjnbujhbngk4eppp9w for details

Migrate to Traefik v2

See merge request picasoft/projets/dockerfiles!53

- Add a custom Dockerfile based on the official one with a HEALTCHECK, psql client and static env variables
- Add a custom entrypoint to automatically run the migrations at first launch only and run migration when updating
- Clean separation of networks
- Adding a tag to fix the version of image
- Configure non-secret environment with Docker Compose
- Update database to PG v12