Add support for gpt-4o model version 2024-11-20

[hardchor]

Why are these changes needed?

Adds support for gpt-4o-2024-11-20

Related issue number

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• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[sonichi]

Thanks. LGTM.

[marklysze]

Great, thanks - looks good.

(Running OpenAI Tests - will check why they're failing. Update: due to it being a fork. All good.)