Improvement: use Doctrine to manage the Reviewer entity

[matks]

In module version 1, the Reviewer model is being persisted in the database using ObjectModel. https://github.com/friends-of-prestashop/demo-cqrs-hooks-usage-module/blob/master/src/Entity/Reviewer.php

In a future version of this module, we could demonstrate the use of Doctrine to handle the database persistence.