add support for arrow notation at child fields level

[scramatte]

Hello,

This PR add support for arrow notation at chield field level allowing the following kind of structure or more complex:

{
  "emails": [
     {
       "attributes": {
         "name": "test",
         "value": "hola mundo"
       }
     }
  ]
}

JsonRepeatable::make('emails')
                ->fields([
                    Text::make('name', 'attributes->name'),
                    Text::make('value'), 'attributes->value'),
                ]),