title: DRF filter choices by group name
body: <p>Let's say I'm making a media library model, and there are these choices in named groups:</p>
  
  <p><code>models.py</code></p>
  
  <pre><code>class MediaLibrary(models.Model):
      MEDIA_CHOICES = [
          ('Audio', (
                  ('vinyl', 'Vinyl'),
                  ('cd', 'CD'),
              )
          ),
          ('Video', (
                  ('vhs', 'VHS Tape'),
                  ('dvd', 'DVD'),
              )
          )
      ]
      media_type = models.CharField(max_length=50, choices=Media_Choices)
  </code></pre>
  
  <p>If I make a request through DRF, it would return all the objects which match either "Audio" and "Video".</p>
  
  <p>How can I filter the request so that it only returns objects under the "Audio" group. (Or the "Video" group.)</p>