Feat: workflow/chatflow api support async

[luckylhb90]

Summary

It does not affect the current usage method. Just by adding one parameter: is_async, the api interface can support asynchronous requests. You just need to poll the new interface to obtain the result. If possible, we may also send the result to kafka after it is available.

[!Tip] Resolve https://github.com/langgenius/dify/issues/13474

Screenshots

Before	After
none	chatflow:
none.	workflow:

Checklist

[!IMPORTANT]
Please review the checklist below before submitting your pull request.

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