Store a file without creating a message

Example response

{
  "id": "clxyz789",
  "messageId": "clxyz123",
  "pluginType": "file",
  "filename": "report.pdf",
  "mimeType": "application/pdf",
  "size": 1024,
  "storageKey": "uploads/clxyz123/report.pdf",
  "createdAt": "2025-01-01T00:00:00.000Z"
}