[Chore][Doc] uses model id determined from OpenAI client

[aarnphm]

This PR cleanups the model id for some structured outputs examples
where before it was hard coded. This PR will determine this model id
from clien such that it will work based on the models users tests with vllm serve

Signed-off-by: Aaron Pham contact@aarnphm.xyz

[github-actions]

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