title: change datetime field to return unix timestamp in django rest framework
body: <p>I want to get a timestamp that is represented in milliseconds or seconds in order to convert it to a DateTime javascript object on the frontend. If there is a way to convert this format
  <code>&quot;timestamp&quot; : &quot;2020-11-06T10: 51: 10Z&quot; </code> to a javascript DateTime object just tell me. If I need to use a separate serializer for the DateTime, how do I use a serializer in a serializer?</p>