optimize(knowledge): Optimize the index logic of the knowledge base

[liuyunchao-1998]

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• This PR title match the format: <type>(optional scope): <description>
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(Optional) Translate the PR title into Chinese.

优化知识库index逻辑

(Optional) More detailed description for this PR(en: English/zh: Chinese).

en:In the past, processing all slices together would pose a challenge to idgen. This adjustment will process slices in batches
zh(optional): 以往将所有的slice放到一起处理，会对idgen产生挑战。本次调整将slice分批处理

(Optional) Which issue(s) this PR fixes:

Fixes #802

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 320 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
backend/domain/knowledge/service/event_handle.go	0.00%	318 Missing ⚠️
...ledge/internal/dal/dao/knowledge_document_slice.go	0.00%	1 Missing ⚠️
backend/domain/knowledge/service/retrieve.go	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
...ledge/internal/dal/dao/knowledge_document_slice.go	24.62% <0.00%> (ø)
backend/domain/knowledge/service/retrieve.go	17.08% <0.00%> (ø)
backend/domain/knowledge/service/event_handle.go	1.61% <0.00%> (-0.63%)	⬇️

... and 4 files with indirect coverage changes

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