[DOCS] Fix list dangling indices documentation (#60099)

This commit fixes the list dangling indices response.
The dangling_indices array is an array of objects
that represent aggregated dangling index information

docs/reference/indices/dangling-indices-list.asciidoc

@@ -38,12 +38,14 @@ The API returns the following response:
 --------------------------------------------------
 {
   "dangling_indices": [
+   {
     "index_name": "my-index-000001",
     "index_uuid": "zmM4e0JtBkeUjiHD-MihPQ",
     "creation_date_millis": 1589414451372,
     "node_ids": [
       "pL47UN3dAb2d5RCWP6lQ3e"
     ]
+   }
   ]
 }
 --------------------------------------------------