title	issue
Fix JWT key generation	NEXT-26164

Core

Changed \Shopware\Core\Maintenance\System\Service\JwtCertificateGenerator to always generate a key 2048 bits long, thus fixing issues when openssl was configured with a different default key length.
Added helper method \Shopware\Core\Checkout\Cart\Event\CartBeforeSerializationEvent::addCustomFieldToAllowList