1. Hold packages at specific versions to prevent unexpected upgrades.
2. Add recommendation to add the current user to the `docker` group to
allow sudo-less usage of the docker commands.
As previously defined, it causes problems as to locally override, one
had also to override the PORTAL_FRONTEND_PORT1 value.
So change the semantic to be only about the base URL, and compose the
whole URL when it is used in the docker-compose file.
Some values which are fixed by the docker compose file should not be set
as variables, and hardcoded everywhere as required.
This also untangles the use of the variables DB_HOST and DB_PORT to be
only about the exposed hostname and port, whenever the DB engine is
exposed on the server interface.
