Change default model and config loading process in AgentBuilder (#917)

* try to fix blog

* modify blog

* fix test error in #717; fix blog typo in installation; update blogs with output examples.

* pre-commit

* pre-commit

* Update website/blog/2023-11-26-Agent-AutoBuild/index.mdx

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>

* add future work

* fix grammar

* update agent_builder

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Co-authored-by: Jieyu Zhang <jieyuz2@cs.washington.edu>
Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>