title: trackingId and clientId with Google tag manager
body: <p>Using analytics.js, i can access to trackingId or clientId with this functions:</p>
  
  <pre><code>ga.getAll()[0].get('trackingId')
  ga.getAll()[0].get('clientId')
  </code></pre>
  
  <p>With Google tag manager, there is no ga object.
  How i can get that parameters?</p>