Add JSON Path based Query Engine (#4595)

* add llama index json path query based index

* update to use jsonpath-ng module for json path query parsing/execution. Update notebook so that it works

* add docstrings + unit tests

* formatting

* remove GPTJSONIndex as it didnt really fit into the paradigm of an index

* updates from PR comments

* fix linting error

* black reformatting

* line length