feat(mail-test): implement email testing functionality

- Created MailTestController to handle email sending requests.
- Added SendTestMailRequest for validating email input.
- Developed MailTestService to manage email sending logic.
- Introduced TestMail Mailable for formatting test emails.
- Defined API route for sending test emails.
- Created EmailIntegrationSeeder to seed email integration settings.
- Updated DatabaseSeeder to include EmailIntegrationSeeder.
- Added MailTestControllerTest to ensure email sending functionality works as expected.

app/Domains/MailTest/Controllers/MailTestController.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Domains\MailTest\Controllers;
+
+use App\Domains\MailTest\Requests\SendTestMailRequest;
+use App\Domains\MailTest\Services\MailTestService;
+use App\Http\Controllers\Controller;
+use Illuminate\Http\JsonResponse;
+
+class MailTestController extends Controller
+{
+    public function __construct(
+        protected MailTestService $mailTestService,
+    ) {}
+
+    public function __invoke(SendTestMailRequest $request): JsonResponse
+    {
+        return response()->json(
+            $this->mailTestService->send(
+                $request->validated('to'),
+                $request->validated('subject'),
+                $request->validated('message'),
+            )
+        );
+    }
+}