waybar: Make output configurable

hosts/miku.nix

@@ -46,7 +46,10 @@
       git.enable = true;
       #gnome-terminal.enable = true;
       tmux.enable = true;
-      waybar.enable = true;
+      waybar = {
+        enable = true;
+        output = "DP-2";
+      };
       xournalpp.enable = true;
       zsh.enable = true;
     };