Add UserValidationByMatrixUsername.

app/Models/Validation/UserValidationByMatrixUsername.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace App\Models\Validation;
+
+use App\Models\Validation\ModelValidationByName;
+use App\Models\Validation\Messages\UserMessagesFactory;
+
+class UserValidationByMatrixUsername extends ModelValidationByName
+{
+    public function __construct(string $name)
+    {
+        parent::__construct(
+            $name,
+            'App\Models\User',
+            (new UserMessagesFactory())->create(),
+        );
+    }
+}