Refactor user option types across modules for consistency

Updated multiple configuration files to replace the user option type with a unified `usersOptionType`, enhancing consistency in user management across applications and services. This change simplifies the user configuration process and improves maintainability.

parts/core.nix

@@ -237,13 +237,20 @@ in
           }) (inputs.self.lib.normalizeUsers users)
         );
       getFirstUser = users: if builtins.isString users then users else (builtins.head users);
-      mergeUsersOption =
-        lib: _loc: defs:
-        let
-          normalize = users: if builtins.isString users then [ users ] else users;
-          allUsers = lib.foldl' (acc: def: acc ++ (normalize def.value)) [ ] defs;
-        in
-        lib.unique allUsers;
+      usersOptionType =
+        lib:
+        lib.mkOptionType {
+          name = "usersOption";
+          description = "Either a single user (string) or multiple users (list of strings)";
+          check = x: builtins.isString x || (builtins.isList x && lib.all builtins.isString x);
+          merge =
+            _loc: defs:
+            let
+              normalize = users: if builtins.isString users then [ users ] else users;
+              allUsers = lib.foldl' (acc: def: acc ++ (normalize def.value)) [ ] defs;
+            in
+            lib.unique allUsers;
+        };
     };
   };
 }