incomplete example to fix #591

[kguelzau]

• use optional dependencies, instead of test dependencies
• https://python-poetry.org/docs/pyproject/#extras

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[nirga]

@kguelzau attaching here the comment from the issue
#591 (comment)

I'm not sure this is the right way to do that - I think this will force the instrumentation to pull an OpenAI dependency, no?