Create Documents Bulk

Bulk upload documents with associated PDF files.

- `documents_metadata`: JSON string matching the DocumentsBulkCreate schema.
Example:
{
    "documents": [
        {
            "reference": "ref1",
            "document_create": { ... },
            "associated_file": "file1.pdf"
        }
    ]
}
- `files`: List of PDF files to upload.

It processes the documents in batches and returns job IDs for tracking.