Add RetrieveChat (#1158)

* Add RetrieveChat notebook, RetrieveAssistantAgent and RetrieveUserProxyAgent

* Update according to comments

* Add output

* Add tests, merge main, address comments

* Fix tests

* Merge main

* Remove unnecessary code

* Update test

* Update notebook, some functions

* Fix print issue

* Update notebook

* Update notebook

* Update notebook

* Improve retrieve utils and update notebook

* Update vector db creation method

* Update notebook

* Update notebook

* Add terminate if no more context

* Update prompt and notebook, add example for update context

* Update results

* Update results

* Update results of update context

* Fix typo

* Add table of contents

* Update table of contents