Add a Blog Post on the AutoGen Assistant (#834)

* add autogenassistant blog post

* update formatting in blog plst

* Fix typo

* Fix typo

* Update title

* Improve language

* Update website/blog/2023-12-01-AutoGenAssistant/index.mdx

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

* Update website/blog/2023-12-01-AutoGenAssistant/index.mdx

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

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Co-authored-by: gagb <gagb@users.noreply.github.com>
Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>
Co-authored-by: Chi Wang <wang.chi@microsoft.com>