[Feature Request] Docker Secret Support

[ShadowPeo]

I would like to see support for Docker Secrets, explicitly utilising the somewhat standard _FILE Suffix for the environmental names.

Whilst I would like to see this as an option for all environment variables, passwords/API Keys/Users/URI's should have this option.

The Secrets function allows for the hiding of secrets which are only passed to the container at runtime, thus allowing the main data to be sent to a public repository for sharing configurations but without the chance of secret information leaking.