title: UNNotificationAttachment with UIImage or Remote URL
body: <p>In my <code>Notification Service Extension</code> I am downloading an image from a URL to show as <code>UNNotificationAttachment</code> in a notification. </p>
  
  <p>So I have this image as UIImage and don't see the need to write it in my app directory / group container on disc just to set up the notification.</p>
  
  <p><strong>Is there a good way create an <code>UNNotificationAttachment</code> with a UIImage ?</strong>
  (should be appliable to local and remote notifications)</p>