Make ckeditor_indentblock compatible with Drupal 10 and CKEditor 5

Enable the IndentBlock functionality included with CKEditor 5 core.

@todo: Implement per-format config to disable IndentBlock.

Closes #3338085

config/schema/ckeditor_indentblock.schema.yml

@@ -5,3 +5,10 @@ ckeditor.plugin.indentblock:
     enable:
       type: boolean
       label: 'Enable'
+ckeditor5.plugin.ckeditor_indentblock_indent:
+  type: config_object
+  label: 'CKEditor IndentBlock settings'
+  mapping:
+    enable:
+      type: boolean
+      label: 'Enable'