waybar: Make output configurable

modules/programs/waybar/default.nix

@@ -5,6 +5,11 @@ let
 in {
   options.ptw.programs.waybar = {
     enable = lib.mkEnableOption "Enable and configure waybar using HomeManager";
+    output = lib.mkOption {
+      type = lib.types.str;
+      example = "DP-2";
+      description = "The output waybar should appear on";
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -15,7 +20,7 @@ in {
         style = builtins.readFile ./style.css;
         settings = [
           {
-            output = [ "DP-2" ];
+            output = [ "${cfg.output}" ];
             layer = "bottom";
             position = "left";
             gtk-layer-shell = true;