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.

.env.example

@@ -51,10 +51,10 @@ REDIS_HOST=127.0.0.1
 REDIS_PASSWORD=null
 REDIS_PORT=6379
 
-MAIL_MAILER=log
-MAIL_SCHEME=null
-MAIL_HOST=127.0.0.1
-MAIL_PORT=2525
+MAIL_MAILER=smtp
+MAIL_SCHEME=smtp
+MAIL_HOST=smtp.gmail.com
+MAIL_PORT=587
 MAIL_USERNAME=null
 MAIL_PASSWORD=null
 MAIL_FROM_ADDRESS="hello@example.com"