[Misc][OpenAI] deprecate max_tokens in favor of new max_completion_tokens field for chat completion endpoint

[gcalmettes]

OpenAI deprecated the max_tokens field in favor of the new max_completion_tokens field for its create chat completion request.

Libraries like Microsoft Semantic-kernel are using the new max_completion_tokens field in their create chat request, leading to a pydantic validation error.

{"object":"error","message":"[{'type': 'extra_forbidden', 'loc': ('body', 'max_completion_tokens'), 'msg': 'Extra inputs are not permitted', 'input': 4096}]","type":"BadRequestError","param":null,"code":400}

This PR marks the max_tokens field as deprecated in the ChatCompletionRequest model (but still supports it) and add the support for the newly max_completion_tokens field, which takes precedence over max_tokens if present in the request.

Tests leveraging create_chat_completion requests have been updated to use the new field.

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[DarkLight1337]

Thanks for updating this, what is the minimum openai-python version that is required to use max_completion_tokens?

[gcalmettes]

@DarkLight1337 good catch!

They added the change with version v1.45.0 when they introduced support for the o1 models.

I have added the bump of the openai version to 1.45.0 in the dependencies

[DarkLight1337]

Thanks for updating this!