Warn or prevent users from unpublishing/deleting Virtual Y Login/Dashboard pages

[froboy]

If a privileged user removes either the Virtual Y Login page or Virtual Y homepage they might accidentally break the site. We should warn users or prevent these actions.

YUSA discussed this and we decided to completely block users from deleting these pages, but not do anything else, mostly for simplicity sake. It may be more desirable to present an interstitial Are you sure you want to do this page if either of these actions is taken.

Our code, for adapting:

/**
 * Implements hook_node_access().
 */
function our_module_node_access(NodeInterface $node, $op, AccountInterface $account) {
  $config = \Drupal::config('openy_gated_content.settings')->getRawData();
  $url = \Drupal::service('path_alias.manager')->getAliasByPath('/node/'. $node->id());
  switch ($op) {
    case 'delete':
      if($url == $config['virtual_y_url'] || $url == $config['virtual_y_login_url']
        || $url == $config['virtual_y_logout_url']) {
        return AccessResult::forbidden();
      } else {
        return AccessResult::neutral();
      }
  }
}