Grok family of models added and is now supported by OpenAIChatCompletionClient...

[M-H-Amini]

Why are these changes needed?

This PR adds support for the Grok family of models to OpenAIChatCompletionClient. The change enables AutoGen users to interact with Grok models using the same interface as other OpenAI-compatible chat models. This improves extensibility and broadens the range of LLMs that AutoGen can work with.

Related issue number

None

Checks

• [X] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• [ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [X] I've made sure all auto checks have passed.