title: Custom error messages in Django Rest Framework serializer
body: <p>The scenario is quite straight-forward:</p>
  
  <p>I have a model with some fields that are required. Let's say one of them is a <code>TextField</code> which can't  be <code>blank</code>.
  I also have a <code>ModelSerializer</code> (Django Rest Framework) that represents that model.</p>
  
  <p>When an empty string is used to set that field through the serializer the error returned comes from the model itself (<code>This field can't be blank</code>).</p>
  
  <p>I would like to override the error messages only in the serializer level, without the need to explicitly re-specifying every field in the serializer (which I believe is against the DRY principle), having to write a <code>validate_</code> method for each field and raise my own <code>ValidationError</code> or having to change the error messages in the <code>Model</code> level (because sometimes the context of the error message matters to my use-case and the error message should be given accordingly).</p>
  
  <p>In other words, is there a way to override error messages in the serializer level as easy as it is for a <code>ModelForm</code>:</p>
  
  <pre><code>class MyModelForm(ModelForm):
      class Meta:
          model = MyModel
          error_messages = {"field1": {"required": _("For some reason this is a custom error message overriding the model's default")}}
  </code></pre>