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/nvidia/default.nix

@@ -0,0 +1,20 @@
+{ lib, pkgs, ... }:
+
+{
+  imports = [
+    ../../../../common/cpu/intel
+    ../../../../common/pc/laptop
+    ../xps-common.nix
+  ];
+
+
+  # This runs only nvidia, great for games or heavy use of render applications
+
+  ##### disable intel, run nvidia only and as default
+  services.xserver.videoDrivers = lib.mkDefault ["nvidia"];
+  hardware.nvidia.modesetting.enable = lib.mkDefault true;
+  hardware.nvidia.optimus_prime.enable = lib.mkDefault true;
+  hardware.nvidia.optimus_prime.nvidiaBusId = lib.mkDefault "PCI:1:0:0";
+  hardware.nvidia.optimus_prime.intelBusId = lib.mkDefault "PCI:0:2:0";
+
+}