Support to read spotify credentials from env variables

[TribuneX]

I tried to use env variables in my config.json:

"spotify": {
            "clientID": "${SPOTIFY_CLIENT_ID}",
            "clientSecret": "${SPOTIFY_CLIENT_SECRET}"
        }

I tried to set these variables on my docker host and pass them to the container with these settings in my docker-compose.yml:

environment: 
        - SPOTIFY_CLIENT_ID=${SPOTIFY_CLIENT_ID}
        - SPOTIFY_CLIENT_SECRET=${SPOTIFY_CLIENT_SECRET}

But magic-cards was unable to get the token from spotify then. I assume that the variables within the config are not resolved by magic-cards at startup?