New Feature 4.2 - Dead Letter Queue (DLQ) feature.

[eschabell]

Document the new Dead Letter Queue (DLQ) feature. A new Dead Letter Queue feature has been added to preserve invalid chunks for later verification and troubleshooting. This helps with:

• Data Preservation: Invalid chunks are preserved instead of being lost
• Troubleshooting: Investigate and debug problematic data without losing it
• Filesystem Storage: DLQ support for filesystem chunks with safe deletion checks

[eschabell]

@esmerel would you mind looking back at the PR work done on this issue?