Add 'POSTGRES_DB=postgres' to the custom example
Add 'POSTGRES_DB=postgres' to the custom example

To fix https://github.com/odoo/odoo/issues/27447. Sort the environtment variables as well.

nats-io/docker-docs,avoinea/docs,31z4/docs,jetty-project/docker-docs,docker-solr/docs,dinogun/docs,jetty-project/docker-docs,tilosp-docker/library-docs,nats-io/docker-docs,Lightstreamer/docs,odoo/docker-docs,tilosp-docker/library-docs,docker-library/docs,docker-solr/docs,dinogun/docs,infosiftr/docker-library-docs,Bonitasoft-Community/docker_docs,docker-library/docs,odoo/docker-docs,31z4/docs,Lightstreamer/docs,Bonitasoft-Community/docker_docs,avoinea/docs,crate/docker-docs,infosiftr/docker-library-docs,crate/docker-docs