More Webhook API Changes

- Updated API Models with Fixes
- Updated Samples
- Additional Functional Tests

sample/notifications/ListWebhooks.php

@@ -0,0 +1,27 @@
+<?php
+
+// # Get All Webhooks Sample
+//
+// Use this call to list all the webhooks, as documented here at:
+// https://developer.paypal.com/webapps/developer/docs/api/#list-all-webhooks
+// API used: GET /v1/notifications/webhooks
+
+// ## List Webhooks
+
+// This step is not necessarily required. We are creating a webhook for sample purpose only, so that we would not
+// get an empty list at any point.
+// In real case, you dont need to create any webhook to make this API call.
+/** @var \PayPal\Api\Webhook $webhook */
+$webhook = require_once __DIR__ . '/../bootstrap.php';
+
+// ### Get List of All Webhooks
+try {
+    $output = \PayPal\Api\Webhook::getAll($apiContext);
+} catch (Exception $ex) {
+    ResultPrinter::printError("List all webhooks", "WebhookList", null, $webhookId, $ex);
+    exit(1);
+}
+
+ResultPrinter::printResult("List all webhooks", "WebhookList",null, null, $output);
+
+return $output;