title: How to create unique delayed jobs
body: <p>I have a method like this one</p>
  
  <pre><code>  def abc
       // some stuff here
    end
    handle_asynchronously :abc, queue: :xyz
  </code></pre>
  
  <p>I want to create a delayed job for this only if there isn't one already in the queue.</p>
  
  <p>I really feel like this should have an easy solution</p>
  
  <p>Thanks!</p>