Adding a test function for OpenAI completion in flaml (#951)

* improve max_valid_n and doc

* Update README.md

Co-authored-by: Li Jiang <lijiang1@microsoft.com>

* add support for chatgpt

* notebook

* newline at end of file

* chatgpt notebook

* ChatGPT in Azure

* doc

* math

* warning, timeout, log file name

* handle import error

* doc update; default value

* paper

* doc

* docstr

* eval_func

* add a test func in completion

* update notebook

* update math notebook

* improve notebok

* lint and handle exception

* flake8

* exception in test

* add agg_method

* NameError

* refactor

* Update flaml/integrations/oai/completion.py

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

* Update flaml/integrations/oai/completion.py

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

* add example

* merge files from oai_eval_test

* Revert "merge files from oai_eval_test"
This reverts commit 1e6a550f913bb94df6e9680934ccb7175d00702e.

* merge

* save results to notebook_output

* update version and cache

* update doc

* save nb cell results to file

* fix typo in model name

* code improvements

* improve docstr

* docstr

* docstr on the Returns of test

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Co-authored-by: Chi Wang <wang.chi@microsoft.com>
Co-authored-by: Li Jiang <lijiang1@microsoft.com>
Co-authored-by: Susan Xueqing Liu <liususan091219@users.noreply.github.com>