title: django admin search by foreign key in add form
body: <p>In the form to add new objects in Django admin, sometimes there are linked foreign keys that are selectable in a dropdown. Is there a way to include a searchbox for the foreign keys within the form?</p>
  <p>For example, let's say I have a Book model with a foreign key to Author object. Instead of scrolling through all the author ids when I create a new Book object, can I search for Author &quot;James&quot; specifically?</p>