Teachability for any agent (#1091)

* Partial implementation

* Partial implementation

* Fixes

* update tests

* cleanup

* update tests

* comments

* logging

* wording

* underscore

* Extend notebook for teachable GPTAssistantAgent

* Notebook for teachable GPTAssistantAgents

* Update notebook

* Update notebook

* Update notebook

* Update notebook

* revert file

* Update blog post and other documentation.

* pre-commit

* Address reviewer feedback.

* Add new nb link to examples page.

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Co-authored-by: Chi Wang <wang.chi@microsoft.com>