Add custom AutoGen LLM client as workaround for missing LiteLLM support

[Shridhar-2205]

• LiteLLM-based LLM wrapper does not provide an AutoGen-compatible model client for different frameworks.​
• Need to implement an explicit AutoGen model client that wraps the existing LiteLLM client.

[jparello]

Not needed we have the multiple LLMs without LiteLLM