DPath extractor enhancement

[artem1205]

Tell us about the problem you're trying to solve

Dpath expects records to be found in list by passing a path to it, e.g. '/data/path_to_records/'.
Facebook Pages returns records inside a nested list, see the example:

{
        "data": [
            {'insights':
                {'data': [
                    {"id": "id1",
                    "name": "name1",
                    ...
                    },
                    {"id": "id1",
                    "name": "name1",
                    ...
                    },
                    ...
            },
            ...
        ]
    }

Describe the solution you’d like

make it possible to deal with lists inside dpath , so that field_pointer will now that next fields will be inside list, e.g. pass extra symbol or empty list.
["data", [], "insights", "data"]

[artem1205]

Implemented in #21690