[Feature Request] Add sample demonstrating how to make liteLLM calls from a workflow

[dandavison]

Add a sample demonstrating how to make LLM calls from a workflow via an activity.
This should use https://github.com/BerriAI/litellm.
(It may make sense to add something like this to SDK contrib/ eventually.)

[jssmith]

The AI Cookbook will contain this sample soon (and others). We could still put a version here, but it might not be necessary.