raise error when msg is invalid; fix docstr; improve ResponsiveAgent; update doc and packaging; capture ipython output; configurable default reply

[sonichi]

Why are these changes needed?

1. raise a ValueError when received msg is not a valid oai message in ResponsiveAgent.
2. fix docstr.
3. allow None to return in genreate_reply().
4. add update_system_message().
5. update doc.
6. add color in print.
7. improve packaging.
8. capture ipython cell output in reply when executing in ipython.
9. find code blocks with llm when regex fails - removed as it doesn't work reliably.
10. make default_auto_reply configurable.

Related issue number

Checks

• [x] 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.
• [x] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [x] I've made sure all auto checks have passed.