Add xps 9560 with its own quirks, I added versions:

1 default one, with nvidia working and intel working, needs optirun to
run application with nvidia
2 intel only, I am using this as my daily driver for long time, only
intel is turned on and nvidia is turned off and doesn't drain any
power.
3 nvidia only, intel is dissabled and nvidia is picked as default gpu,
no need to fiddle with optirun etc, good for gpu heavy application.

All these settings needs to reboot to work properly

dell/xps/15-9560/intel/default.nix

@@ -0,0 +1,18 @@
+{ lib, pkgs, ... }:
+
+{
+  imports = [
+    ../../../../common/cpu/intel
+    ../../../../common/pc/laptop
+    ../xps-common.nix
+  ];
+
+
+  # This runs only Intel and nvidia does not drain power.
+
+  ##### disable nvidia, very nice battery life.
+  hardware.nvidiaOptimus.disable = lib.mkDefault true;
+  boot.blacklistedKernelModules = lib.mkDefault [ "nouveau" "nvidia" ];
+  services.xserver.videoDrivers = lib.mkDefault [ "intel" ];
+
+}