Support custom text formats and recursive (#496)

* Add custom text types and recursive

* Add custom text types and recursive

* Fix format

* Update qdrant, Add pdf to unstructured

* Use unstructed as the default text extractor if installed

* Add tests for unstructured

* Update tests env for unstructured

* Fix error if last message is a function call, issue #569

* Remove csv, md and tsv from UNSTRUCTURED_FORMATS

* Update docstring of docs_path

* Update test for get_files_from_dir

* Update docstring of custom_text_types

* Fix missing search_string in update_context

* Add custom_text_types to notebook example