feat: switch to chat messages before regenerated

[xuzuodong]

Summary

This PR implements a new feature that allows users to switch and check messages before regenerated.

Screenshots

Agent App in Explore page	2024-12-03.17.33.21.mov
Chatflow in running app	2024-12-05.17.18.47.mov

PR Stack

• feat: switch to chat messages before regenerated (This PR)
• feat: regenerate history switch navigation #8749
• feat: regenerate in Chat, agent and Chatflow app #7661

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods