Google analytics script: add and setup

<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-167311748-1"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());
  gtag('config', 'UA-167311748-1');
</script>

GA code for the production

1. Implement Google Analytics
2. Important: disable gathering of sensitive user information via google analytics (bidder token and additional parameters, if needed)
3. Debug Google Analytics code on dev or sandbox and check whether all information is gathered correctly

Next steps:

1. Add tracking events to google analytics (in separate tasks for each auction types)