title: Django: FileField, missing content_type
body: <p>If I read the docs correctly, then the FileField in Django does not know the content_type of the file: <a href="https://docs.djangoproject.com/en/2.1/ref/models/fields/" rel="nofollow noreferrer">https://docs.djangoproject.com/en/2.1/ref/models/fields/</a></p>
  
  <p>I would like to store files in a Django application, but I want to query the content_type.</p>
  
  <p>Examples:</p>
  
  <ul>
  <li>list all objects which have a file with content_type "application/pdf"</li>
  <li>list all objects which have a file with content_type "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"</li>
  </ul>
  
  <p>What is the most django-like way to handle this?</p>