Support KeyValue Type for Ruby PHP and Python

Summary: Add support of type KeyValue to Ruby, PHP, and Python.

Reviewed By: mengxuanzhangz

Differential Revision: D53016094

fbshipit-source-id: 50409b3f7f5f8df38853e266edf46e781c269a47

src/FacebookAds/Object/Fields/LeadgenFormFields.php

@@ -70,7 +70,7 @@ public function getFieldTypes() {
       'questions' => 'list<LeadGenQuestion>',
       'status' => 'string',
       'thank_you_page' => 'LeadGenThankYouPage',
-      'tracking_parameters' => 'list<map<string, string>>',
+      'tracking_parameters' => 'list<KeyValue>',
     );
   }
 }