Setup ab test experiment debugger

MAILPOET-4972

mailpoet/lib/Features/FeaturesController.php

@@ -9,11 +9,14 @@ class FeaturesController {
 
   const FEATURE_COUPON_BLOCK = 'Coupon block';
 
+  const LANDINGPAGE_AB_TEST_DEBUGGER = 'landingpage_ab_test_debugger';
+
   // Define feature defaults in the array below in the following form:
   //   self::FEATURE_NAME_OF_FEATURE => true,
   private $defaults = [
     self::FEATURE_HOMEPAGE => false,
     self::FEATURE_COUPON_BLOCK => false,
+    self::LANDINGPAGE_AB_TEST_DEBUGGER => false,
   ];
 
   /** @var array|null */