update notebook with new models

[sonichi]

Why are these changes needed?

1. test and update agent notebook examples with the new openai models.
2. update the version.
3. a small modification of the system prompt of assistant agent.
4. a new notebook example with a planning agent.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/FLAML/. See https://microsoft.github.io/FLAML/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.