Add Japanese documentation(template.ja.mdx) for Knowledge API

[yagiyuki]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

The Knowledge API documentation is currently not available in Japanese. On the other hand, the chat and workflow apps are already localized in Japanese and are easy to use for Japanese-speaking users. To improve accessibility and usability, I think the Knowledge API should also provide documentation in Japanese (template.ja.mdx).
https://github.com/langgenius/dify/tree/1fa66405c5e89acfbb031142e49ae2ffa5e67efb/web/app/(commonLayout)/datasets/template

2. Additional context or comments

#12247 (comment)

3. Can you help us with this feature?

• I am interested in contributing to this feature.