DocumentMetadata

Document metadata containing content and chunking information.

This class stores metadata about a document chunk, including the content (which can be text, image, video, etc.), document ID, chunk ID, and optional custom payload fields.

The content field uses ContentBlock which is a sealed hierarchy supporting different content types (TextBlock, ImageBlock, VideoBlock, etc.).

The payload field allows storing custom metadata such as file name, department, author, creation time, tags, and other business-specific fields. These fields are stored as key-value pairs and will be persisted to vector databases along with the document content.

Example usage with payload:

`Map<String, Object> payload = new HashMap<>();
payload.put("filename", "report.pdf");
payload.put("department", "Finance");
payload.put("author", "John Doe");
payload.put("created_at", "2024-01-15T10:30:00Z");
payload.put("tags", Arrays.asList("urgent", "quarterly"));

TextBlock content = TextBlock.builder().text("Document content").build();
DocumentMetadata metadata = new DocumentMetadata(content, "doc-123", "chunk-0", payload);
`