Resolve #2978703 "Support matomo tag"

Closes #2978703

js/matomo_tag_manager.js

+/**
+ * @file
+ * Attaches Matomo Tag Manager to the page.
+ */
+
+(function (settings) {
+
+  "use strict";
+
+  var _mtm = window._mtm = window._mtm || [];
+  _mtm.push({'mtm.startTime': (new Date().getTime()), 'event': 'mtm.Start'});
+  var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
+  g.type='text/javascript'; g.async=true; g.src=settings.matomo.matomoUrl+'/js/container_'+settings.matomo.containerId+'.js'; s.parentNode.insertBefore(g,s);
+
+})(drupalSettings);