title: Nifi convert UTC to unix time
body: <p>I have a flowfile attribute which is a UTC datetime in the format of yyyy-MM-dd HH:mm:ss.SSS</p>
  <p>I need to convert this to a unix timestamp.</p>
  <p>How can this be done? I know its possible to convert Unix to the above format using Jolt:</p>
  <p>&quot;time&quot;: &quot;${time:format('yyyy-MM-dd HH:mm:ss.SSS')}&quot;</p>
  <p>however, im not sure how to do this in reverse?</p>