nixos/navidrome: add openFirewall option

This adds an option to the navidrome module to open the configured TCP
port in the firewall.

nixos/modules/services/audio/navidrome.nix

···
         '';
       };
 
+      openFirewall = mkOption {
+        type = types.bool;
+        default = false;
+        description = lib.mdDoc "Whether to open the TCP port in the firewall";
+      };
     };
   };
 
   config = mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = mkIf cfg.openFirewall [cfg.settings.Port];
+
     systemd.services.navidrome = {
       description = "Navidrome Media Server";
       after = [ "network.target" ];