Add regenerate message example

[warrenmblood]

We currently do not have any functional examples of a "regenerate message" action button in a message footer like so:

Acceptance Criteria:

• Add an example showcasing a "regenerate" button in a chatbot message footer utilizing the custom_footer_slot (See this PR adding support for custom footers).
• Regenerate button should actually trigger the chat to send a new response
• Add example(s) for both React & WC

[ethanwinters]

This would be "simple" regenerate. e.g. "delete current response and resend to the previous request". Not sure how folks are supposed to access the "request message" so we would need to think ahead towards "what does a full OOTB regenerate story with the ability to navigate back to other messages" looks like.