Add possibility to attach PDF files to the e-mail

I wrote about our approach in a MR.

A get an error on "/admin/commerce/config/emails" page after add MR!25 :

ArgumentCountError: Too few arguments to function Drupal\commerce_email\EmailSender::__construct(), 4 passed in /var/www/html/web/core/lib/Drupal/Component/DependencyInjection/Container.php on line 261 and exactly 5 expected in Drupal\commerce_email\EmailSender->__construct() (line 77 of modules/contrib/commerce_email/src/EmailSender.php).

By adding the create method inside the EmailSender class, this works:

public static function create(ContainerInterface $container) {
  return new static(
    $container->get('commerce_email.mail_handler'),
    $container->get('token'),
    $container->get('database'),
    $container->get('entity_type.manager'),
    $container->get('event_dispatcher')
  );
}

In fact, this MR works really well, it's great.
Do you think it would be easy to modify to be able to select several files in the list, for example a pdf of the order and another from the store?