Add customEvent:Rating dimension to gtag (#2777)

To be able to get the rating data through the Google Data API, we need to send the value to the customEvent:Rating dimension

Author: svekars

_templates/layout.html

@@ -85,11 +85,11 @@
       tutorialTitle: $('h1:first').text(),
       rating: $(this).attr("data-count")
     });
-
     gtag('event', 'click', {
       'event_category': 'Tutorial Rating',
       'event_label': $("h1").first().text(),
-      'value': $(this).attr("data-count")
+      'value': $(this).attr("data-count"),
+      'customEvent:Rating': $(this).attr("data-count") // send to GA custom dimension customEvent:Rating.
     });
    });