Exposing all config values will allow users to skip setting environment variables twice - once as a docker option and once as an env var. Docker will automatically pull the value from the environment if none is set for the --build-arg flag.
Users will still be required to specify each desired env var via --build-arg as otherwise docker builds will complain about unused build arguments.
Re-implements #5978 (lost in a rebase)
Closes#5903
94f4d1325c