feat(analytics): AB testing

User model update for AB tests, and the first AB test to start Sept 12

closes #7984

website/server/libs/analyticsService.js

@@ -85,6 +85,10 @@ let _formatUserData = (user) => {
     properties.subscription = user.purchased.plan.planId;
   }
 
+  if (user._ABtest) {
+    properties.ABtest = user._ABtest;
+  }
+
   return properties;
 };