title: Change Django ModelChoiceField to show users' full names rather than usernames
body: <p>I have a form in my Django app (not in admin) that allows staff members to select a user from a dropdown.</p>
  
  <pre><code>forms.ModelChoiceField(queryset = User.objects.filter(is_staff=False), required = False)
  </code></pre>
  
  <p>The problem is that the dropdown shows users by usernames whereas I'd rather it show their full name from user.get_full_name() and use username only if that is not available. I only really need this change on this page, in other places like admin, I don't care if it uses username.</p>
  
  <p>Is there a way I can do this?</p>
  
  <p>Thanks!</p>