title: Django: Annotate list of related fields
body: <p>I have an Company and User models with a related model CompanyRecruiter:</p>
  
  <pre class="lang-py prettyprint-override"><code>class CompanyRecruiter(models.Model):
  
      organization = models.ForeignKey(Company, related_name="company_recruiters")
      recruiter = models.ForeignKey(User, related_name="company_recruiters")
  </code></pre>
  
  <p>I want to annotate the list of user ids of users who are recruiters for companies to be able to filter on them later:</p>
  
  <pre class="lang-py prettyprint-override"><code>Company.objects.annotate(some_stuff=some_other_stuff).values_list("user_ids", flat=True)
  # [ [1, 2], [1, 56], [] ]
  </code></pre>
  
  <p>I already tried with Custom Aggregates and Subqueries without success.
  I use postgres.</p>