Properly treat secrets in Dockerfile

[ronaldtse]

https://docs.docker.com/develop/develop-images/build_enhancements/

https://stackoverflow.com/questions/55789409/how-to-unset-env-in-dockerfile/55789497

[CAMOBAP]

Actually, ARGs don't recommend to pass sensitive information at all

• https://docs.docker.com/engine/swarm/secrets/#about-secrets
• https://pythonspeed.com/articles/docker-build-secrets/

In progress

[CAMOBAP]

Done