docs: update docs for the afcl modal

Author: yaroslav8765

adminforth/documentation/docs/tutorial/03-Customization/15-afcl.md

@@ -2417,6 +2417,8 @@ import { Modal, Button } from '@/afcl';
   askForCloseConfirmation?: boolean // Show extra popup to confirm close ( to avoid close by accident)
   closeConfirmationText?: string // Text that will be shown on close confirmation popup
   removeFromDomOnClose?: boolean // Remove modal from DOM on close ( default is false )
+  backgroundCustomClasses?: string // allows to add custom classes to the gray background of modal (e.g. you can have bg-pink-500/60)
+  modalCustomClasses?: string // allows to add custom classes to modal popup
 ```
 
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