Help text for only users who have permission

@codechefmarc thanks for your contribution.
I need to fix autotests first, but your MR will be reviewed and merged asap.

Quick update: I've rebased the MR with 2.0.x to re-run fixed tests. As expected no problem with this minor update, however, I would like to check if that possible to rewrite the piece of code using a better approach.

In case of failure, I will merge this MR as it is.

Related issue from core: https://www.drupal.org/project/drupal/issues/3522629 ✨ Provide access to protected properties in ConfigureSectionForm through getter methods Active

The patch looks ok to me. I would have used #access property on the render array to make this a bit more cleaner to read but thats just by gusto:

    $form['layout_settings']['layout_builder_lock_info'] = [
      '#markup' => '<p>' . t('Locks can be configured when the section has been added.') . '</p>',
      '#weight' => 100,
      '#access' => \Drupal::currentUser()->hasPermission('manage lock settings on sections'),
    ];

Maybe form decorator approach would make this even cleaner https://www.drupal.org/project/form_decorator → but this would be out of scope of this issue for sure.

@hydra good point, I'll update MR