Adding webhook for Apple's ServerToServerNotifications processing

- Processor checks and renews Apple subscription based on the
received notification.
- Since there's no way how to pass user-related data to payment
payload, user is matched against original transaction ID that
should be stored in payment_meta. Module expects app to call
an internal API that sets this meta value for selected user.
- Receipt validation was also added to internal
`verify-purchase` API handler.

src/model/Repositories/PaymentMetaRepository.php

@@ -82,6 +82,16 @@ final public function findByMeta(string $key, string $value)
  ])->fetch();
  }
 
+ final public function findAllByMeta(string $key, string $value)
+ {
+ return $this->getTable()->where([
+ 'key' => $key,
+ 'value' => $value
+ ])
+ ->order('id DESC')
+ ->fetchAll();
+ }
+
  /**
  * @param ActiveRow $payment
  * @param string $key