Path to file containing the secret key base. A new secret key base can be generated by running:
nix build -f '<nixpkgs>' dawarich; cd result; bin/bundle exec rails secret
This file is loaded using systemd credentials, and therefore does not need to be owned by the dawarich user.
If this option is null, it will be created at /var/lib/dawarich/secrets/secret-key-base with a new secret key base.