Allow API_KEY vars to be set from docker secret paths

[a3gill]

Pretty straight-forward. Allow setting API Keys with Docker secrets.
Either allow any VARNAME to be set from the contents of a file path assigned to FILE__VARNAME, or create optional vars for each API KEY var named VARNAME_FILE that accepts a file path that will result in setting VARNAME to the cat result of the supplied path.

Thanks!

[Flaminel]

Are you available to test this when it's implemented?

[Flaminel]

^bump

Unless you're willing to test the implementation, I'm going to close this soon.