title: Add nofollow attribute to each <a> tag with external link after the page was rendered
body: <p>Customer has requested, that all links to external pages in our sitecore solution should have a <em>nofollow</em> attribute. Which pipeline should I use to have an access to response html (to change the links before they will be delivered with markup to browser)? Or is there any better solution to accomplish this?</p>
  
  <p>JavaScript is not much helpful here because I am not sure if all search engines are able to run JavaScript.</p>
  
  <p><em>RenderField</em> processor is also not usable, due to many custom  tags in our code </p>