feat: Add support for custom Q&A in the knowledge base #10873

[dajianguo]

Summary

I need to import some Q&A text，not need LLM to generate results for me。
I modified the code to support excel and csv uploading qa files。
The processing logic is that when there are only two columns in csv or excel and qa mode is selected, the LLM will not be called。

Resolves #4664
Resolves #6904
Resolves #7735
Resolves #7430
Resolves #10873

Screenshots

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]

This one doesn't seem very generic.

[dajianguo]

Is this the separator? "Q00001:" and "A00001:"? I can change to a common separator.

[dajianguo]

I refer to the format_split_text method。

[dajianguo]

It is only a runtime delimiter variable and does not actually store

[crazywoola]

@JohnJyong

[AkisAya]

this should not be done by implicitly change QA LLM mode to a normal QA extraction by a template.
i think user should choose to disable llm QA mode when import file on ui.

something like this

and if user choose to generate QA pair by template, ui shows a hint what template should be according to the file extension

[kiendn1]

I think u shouldn't modify function create_documents, instead of that, create a separate splitter QASplitter

[crazywoola]

I discussed with @JohnJyong, we decide not to merge this PR. If you have any other questions, please feel free to contact with @JohnJyong