title: Include an external id when creating Zendesk support ticket via a Feedback tab
body: <p>I've been able to successfully set up a Feedback Tab for Zendesk on my site and use it to allow users to create support tickets.  My problem, however, is that I'd like to be able to track tickets by user id (which Zendesk usually calls an "external_id").  </p>
  
  <p>I've tried to add "external_id" to the Feedback Tab configuration, but that doesn't appear to have any effect.  Is there any way to accomplish this without coding my own feedback interface?</p>