dustbowl: add greetd + gtkgreet

nixos/dustbowl.nix

@@ -255,6 +255,38 @@
     (callPackage ./posy-cursor-black.nix { })
   ];
 
+  services.greetd = {
+    enable = true;
+    settings = {
+      terminal = {
+        vt = 1;
+      };
+
+      default_session = {
+        command = "${pkgs.sway}/bin/sway --config /etc/greetd/sway-config";
+        user = "greeter";
+      };
+    };
+  };
+  environment.etc."greetd/environments".text = ''
+    ${pkgs.sway}/bin/sway
+  '';
+  environment.etc."greetd/sway-config".text = ''
+    # `-l` activates layer-shell mode. Notice that `swaymsg exit` will run after gtkgreet.
+    exec "${pkgs.gtkgreet}/bin/gtkgreet -l; swaymsg exit"
+
+    bindsym Mod4+shift+e exec swaynag \
+    	-t warning \
+    	-m 'What do you want to do?' \
+    	-b 'Poweroff' 'systemctl poweroff' \
+    	-b 'Reboot' 'systemctl reboot'
+
+    include /etc/sway/config.d/*
+
+    # contains display scaling and keyboard layouts
+    include /etc/sway/localconfig
+  '';
+
   services.flatpak.enable = true;
 
   services.gnome.gnome-keyring.enable = true;