Extract simple workers common code into a base class [PREMIUM-4]

lib/Cron/Workers/KeyCheck/PremiumKeyCheck.php

@@ -0,0 +1,21 @@
+<?php
+namespace MailPoet\Cron\Workers\KeyCheck;
+
+use MailPoet\Models\Setting;
+use MailPoet\Services\Bridge;
+
+if(!defined('ABSPATH')) exit;
+
+class PremiumKeyCheck extends KeyCheckWorker {
+  const TASK_TYPE = 'premium_key_check';
+
+  function checkProcessingRequirements() {
+    return Bridge::isPremiumKeySpecified();
+  }
+
+  function checkKey() {
+    $premium_key = Setting::getValue(Bridge::PREMIUM_KEY_STATE_SETTING_NAME);
+    $result = $this->bridge->checkPremiumKey($premium_key);
+    return $result;
+  }
+}