Make the name of the setup user look more Windows like

lib/modules/windows.nix

@@ -1,4 +1,4 @@
-{ lib, ... }:
+{ lib, config, ... }:
   let
     inherit (lib)
       mkOption
@@ -7,9 +7,20 @@
       types
     ;
 
+    setupUser = lib.strings.stringToCharacters config.valhalla.setupUser.name;
+
     winType = types.submodule (
       { config, ... }: {
         options = {
+          setupUser = mkOption {
+            type = types.str;
+            description = "The name of the user for setting up Windows.";
+            default = lib.strings.concatStrings (
+              [(lib.strings.toUpper (builtins.elemAt setupUser 0))] ++
+              (lib.lists.drop 1 setupUser)
+            );
+          };
+
           dualboot = {
             enable = mkEnableOption "dual boot";