fix: document extractor node incorrectly handles doc and ppt files

[AugNSo]

Summary

Fixes #12889

1. In the current code, document extractor node was using python-docx library to handle doc files, which it cannot process. this commit is trying to use unstructured API to handle doc files.
2. In the current code, document extractor node is using partititon_ppt to handle ppt files, probably a leftover when unstructured[ppt] was still in pyproject.toml. This commit is trying to use unstructured API to handle ppt files.

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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

[AugNSo]

I'm a bit uncertain whether to remove partition_ppt from the code, it does not work anymore but not sure what type of error should be returned if UNSTRUCTURED_API_URL and UNSTRUCTURED_API_KEY is not provided, the same goes with doc processing logic.

[crazywoola]

Please fix the lint errors by running dev/reformat.

[AugNSo]

Please fix the lint errors by running dev/reformat.

Did not manage to run dev/reformat but I assume running ruff check --fix ./api and ruff format ./api should have the same effect since I did not edit .env files (ruff version 0.9.2)? Anyway the two python files I edit has been ruff formatted。