fix: same chunk insert deadlock

[huangzhuo1949]

Summary

Distribute documents into multiple groups based on the hash values of page_content.
This is done to prevent multiple threads from processing the same document, thereby avoiding potential database insertion deadlocks.

fix #12481

Tip

Close issue syntax: Fixes #<issue number> or Resolves #<issue number>, see documentation for more details.

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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

[crazywoola]

Please fix the tests.

[huangzhuo1949]

Please fix the tests.

done~