Summary

set default max_chunks to 1 as others close #10936

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[!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