Allow recipe to add multiple buttons to CKEditor toolbar

Fully agreed that we need this. I can get this written pretty fast.

Using this:

    editor.editor.content_format:
      addItemsToToolbar:
        -
          item_name: aickeditor
        -
          item_name: aiAgentButton

I get the error:

PHP Fatal error:  Cannot declare class Drupal\ckeditor5\Plugin\ConfigAction\AddItemToToolbar, because the name is already in use in /var/www/docroot/core/modules/ckeditor5/src/Plugin/ConfigAction/AddItemsToToolbar.php on line 16

Tested the patch manually and it worked for my site.

Please keep the standard issue summary second, it makes it easier to review as the issue progresses.

I think this will be a great addition!

Php Stan is failing for covers and one question in the MR.