boreal: setup sddm theme module

modules/default.nix

@@ -0,0 +1,6 @@
+{ ... }:
+{
+  imports = [
+    ./sddm.nix
+  ];
+}

modules/sddm.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.my.displayManager.sddm;
+in
+{
+  options.my.displayManager.sddm.enable = lib.mkEnableOption "SDDM setup";
+
+  config = lib.mkIf cfg.enable {
+    services.xserver.displayManager.sddm = {
+      enable = true;
+      theme = "sugar-candy";
+    };
+
+    environment.systemPackages = with pkgs; [
+      packages.sddm-sugar-candy
+
+      # dependencies for sugar-candy theme
+      libsForQt5.qt5.qtgraphicaleffects
+      libsForQt5.qt5.qtquickcontrols2
+      libsForQt5.qt5.qtsvg
+    ];
+  };
+}