Refactor NPS tracking data fetching to use API call

[MAILPOET-1815]

lib/API/JSON/v1/Analytics.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace MailPoet\API\JSON\v1;
+
+use MailPoet\Analytics\Reporter;
+use MailPoet\API\JSON\Endpoint as APIEndpoint;
+use MailPoet\Config\AccessControl;
+
+if (!defined('ABSPATH')) exit;
+
+class Analytics extends APIEndpoint {
+
+  /** @var Reporter */
+  private $reporter;
+
+  public $permissions = array(
+    'global' => AccessControl::NO_ACCESS_RESTRICTION
+  );
+
+  function __construct(Reporter $reporter) {
+    $this->reporter = $reporter;
+  }
+
+  function getTrackingData() {
+      return $this->successResponse($this->reporter->getTrackingData());
+  }
+}