Allow php_opcache to have any number of extra options

[laurentdavid]

Aim of this patch is to allow other configuration values to be added to opcache without having to change the base php role values (https://www.php.net/manual/fr/opcache.configuration.php)

• Use a dictionary instead of a fixed set of variables
• Add the default php_opcache_defaults values

Ensure we have a default value for php_opcache dictionary