feat(plasma): sddm kcm cause thats not default for whatever reason

systems/nel-desktop/configuration.nix

···
-{ ... }: {
+{ pkgs, ... }: {
   imports = [
     ../../modules/nixos
     ./hardware-configuration.nix
···
 
   services.displayManager.sddm.enable = true;
   services.desktopManager.plasma6.enable = true;
+  environment.systemPackages = [ pkgs.kdePackages.sddm-kcm ];
 
   services.pulseaudio.enable = false;
   security.rtkit.enable = true;