title: Only download changes to git repo in VSTS release pipeline
body: <p>I have a VSTS release pipeline that copies files from a git repo:</p>
  
  <p><a href="https://i.stack.imgur.com/oedIV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oedIV.png" alt="enter image description here"></a></p>
  
  <p>This git repo is really big - around 1GB in size.  Every time I trigger a release, the VSTS agent downloads the entire contents of the git repo.  Is there a way to configure VSTS to only download the <em>changes</em> to this git repo, i.e. run a <code>git pull</code> on the repository?  This would save a lot of time and bandwidth.</p>