Ability to fine tune custom model on conversable agents (#1787)

* uAbility to update_model on conversable agents

* formatting

* formatting

* move code from conversable agent into samples/tools and add testing and README

* forgot install step

* fix

* leave core lib unchanged and move everything to samples/tools

* remove skip openai

---------

Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>