fix: http_request node form-data support array[file]

[Sakura4036]

Summary

Fixes: #15326, http_request node form-data support array[file] now.

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

[crazywoola]

I think the changes should be adapt to frontend UI as well.

• file
• array[file]

[Sakura4036]

I think the changes should be adapt to frontend UI as well.

• file
• array[file]

Maybe we don't need to change the frontend UI, the form only supports File and Text types, and the File type supports a single file or a list of files, just like Postman. In my tests, the frontend UI works fine and displays the file types correctly，and the http request with files is sent successfully.

Postman Form