This setup chooses to avoid the env_file option available for Docker
Compose files. Docker has a peculiar way of parsing variables which
makes it, for example, include quotes verbatim.
This is both confusing and incompatible with shells parsing the same
file which is a requirement. For this reason, the configuration does
not import the complete environment using env_file but assigns variables
explicitly on a need-to-know basis in the YAML file, much like Docker
secrets.
Since the configuration is generated automatically, the burden on users
is the same as with env_file: they only need to edit .env for
customizations.
