[site-reviews-forms] enable Custom Fields meta box and unprotect custom fields

/**
 * Enable the Custom Fields metabox for reviews
 * @return void
 */
add_action('admin_init', function () {
    add_post_type_support('site-review', 'custom-fields');
});

/**
 * Unprotect "_custom_*" meta_keys
 * @param bool $protected
 * @param string $metakey
 * @return bool
 */
add_filter('is_protected_meta', function ($protected, $metakey) {
    $prefix = '_custom_';
    if (0 === strncmp($metakey, $prefix, strlen($prefix))) {
        return false;
    }
    return $protected;
}, 10, 2);