Streaming example for the updated OpenAI API

[triakshunn]

Description

This PR updates the usage of the OpenAI API in accordance with the changes in version 1.0.0. The deprecated openai.ChatCompletion has been replaced with client.ChatCompletion.create().

Additionally, the way we extract the content from the API response has been updated. Previously, we checked if the length of chunk['choices'][0]['delta'] was not zero. Now, we check if chunk.choices[0].delta.content is not None before appending it to partial_message.

Closes: #7242

[gradio-pr-bot]

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[abidlabs]

LGTM thanks for the contribution @triakshunn!