Update OpenAI model and API call

[aaravnavani]

This PR fixes this issue and updates 2 things:

1. Instead of text-davinci-003, the model is now gpt-3.5-turbo-instruct as suggested in this OpenAI forum post.
2. Instead of openai.Completion.create, the api call is now openai.completions.create

[zsimjee]

This is great! Thank you for the update, ready to merge once the notebooks complete their checks

[codecov-commenter]

Codecov Report

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Additional details and impacted files

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  Coverage        ?   82.91%           
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  Hits            ?     4775           
  Misses          ?      984           
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unittests	82.91% <0.00%> (?)

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[zsimjee]

Hi, thanks for the PR. We're planning on dropping openai v0 support in our next minor release - 0.5.0. That should minimize the changes we need to make on this PR, let's reassess if we need this PR after that change is in

[zsimjee]

updated as part of latest sprint