Is your feature request related to a problem? Please describe.
I do version control and publish my .config directory in a GitHub repo, as quite a lot of people do. Thus, Due to the inclusion of the client_id, this results in having to gitignore the ~/.config/spotify_player/app.toml, as otherwise the id would be leaked.

Describe the solution you'd like
Save client_id outside the app.toml, so the remainder of the spotify-player-config can be stored in a public git repo without any trouble.

The client_id could then be read from an environment variable, which one could save in .zshenv.

Alternatively, support something like the password_cmd from spotifyd: https://docs.spotifyd.rs/config/File.html

# This is an alternative to the `password` field. Both
# can't be used simultaneously.
password_cmd = "command_that_writes_password_to_stdout"

Describe alternatives you've considered

• gitignoring the app.toml and manually updating it all the time.
• symlinking the app.toml into a private cloud storage.