The environment variables PGUSER, PGPASSWORD, and PGDATABASE are used
instead of POSTGRES_USER, POSTGRES_PASSWORD and POSTGRES_DB. This is so
that those environment variables can be defined in a docker-compose.yml file
for the database container and then be inherited by other services that need
to connect to the database so that they can just define PGHOST to the name of
the database container and then use 'psql' without any connection parameters.
pg_hba.conf is changed to restrict external access to the database to
'samenet' instead of 'all'. This makes it so that other containers in the
deployment can connect to it, but other external addresses are not able to.
pgcli is installed as an alternative to the built-in
psql command.