Add Google Tag Manager scripts to head and body templates

themes/classic/templates/_partials/head.tpl

@@ -109,4 +109,11 @@
       s.parentNode.insertBefore(c,s);
   })(document);
 </script>
+<!-- Google Tag Manager -->
+<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
+new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
+j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
+'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
+})(window,document,'script','dataLayer','GTM-PCWJ25RQ');</script>
+<!-- End Google Tag Manager -->
 {/literal}