title: How to filter based on the last element in ArrayField in django
body: <p>I'm using postgresql database which allows having an array datatype, in addition django provides PostgreSQL specific model fields for that. 
  My question is how can I filter objects based on the last element of the array?</p>
  
  <pre><code>class Example(models.Model):
       tags = ArrayField(models.CharField(...))
  example = Example.objects.create(tags=['tag1', 'tag2', 'tag3']
  example_tag3 = Example.objects.filter(tags__2='tag3')
  </code></pre>
  
  <p>I want to filter but don't know what is the size of the tags. Is there any dynamic filtering something like:</p>
  
  <pre><code>example_tag3 = Example.objects.filter(tags__last='tag3')
  </code></pre>