feat: AI-OCR for PDFs

[fsatsuki]

Issue #, if available:

Using AI for PDF OCR

Description of changes:

PDFs contain various types of images, graphs, charts, designs, objects, etc., and these PDFs are easy for people to understand. However, typical OCR tools can't understand relationships between objects. Tabular tables are single-column strings, so it's difficult to infer table relationships from strings. The AI-OCR feature converts PDFs to images one by one and supports OCR using Claude3's multimodal features. As a result, structured markdown text can be retrieved and used as RAG knowledge.

The DB schema has changed. Add “Metadata” as JSON. In this PR, images converted from PDFs are stored in S3 buckets. It is placed in the source image URL and placed in the original pdfurl of the metadata.parentSource.

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[statefb]

Memo: When the bedrock knowledge base retrieve api supports detail reference chunk, this PR could be a good reference.