Feat: Add support for pgvector with Japanese keyword search

[utsumi-fj]

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

When using pgvector for vector store, keyword search, which should work by Retrieval Setting Full-Text Search and Hybrid Search, in Japanese is not supported.

For now, keyword search with pgvector uses tsvector which does not support Japanese by default.

2. Additional context or comments

No response

3. Can you help us with this feature?

• [x] I am interested in contributing to this feature.