Merge branch 'add-event-tracking-for-canary-deploys' into 'master'

Adding additional snowplow event tracking

See merge request gitlab-org/gitlab-ee!12088

ee/app/views/layouts/_snowplow.html.haml

@@ -20,3 +20,5 @@
 
   window.snowplow('enableActivityTracking', 30, 30);
   window.snowplow('trackPageView');
+
+= render 'layouts/snowplow_additional_tracking'

ee/app/views/layouts/_snowplow_additional_tracking.html.haml

+- return unless Feature.enabled?(:additional_snowplow_tracking)
+
+:javascript
+  window.snowplow('enableFormTracking');
+  window.snowplow('enableLinkClickTracking');