Add pipeline DLQ support for rds source

[oeyh]

Description

Adds pipeline DLQ support to the RDS source plugin for both the stream path (binlog/WAL) and the export path.

When a dlq_pipeline is configured, failed events are sent to it with _failure_metadata containing pluginId, pluginName, pipelineName, and errorMessage.

Stream path (BinlogEventListener / LogicalReplicationEventProcessor):

• Row processing failures (data type conversion, record conversion)
• Buffer write/flush failures

Export path (DataFileLoader):

• Record processing failures during parquet file loading

When no dlq_pipeline is configured, behavior is unchanged — errors are logged and counters incremented.

Testing

Tested end-to-end locally against Aurora MySQL with a dlq_pipeline configured with a stdout sink.

Stream path:

• Verified normal INSERT/UPDATE/DELETE events flow to the main pipeline with no DLQ output
• Triggered row processing error and confirmed the failed event was sent to the DLQ with correct _failure_metadata

Export path:

• Ran a full RDS export and verified records are processed normally
• Triggered row processing error and confirmed failed events were sent to the DLQ with correct _failure_metadata

No DLQ configured:

• Verified that when no dlq_pipeline is defined, failurePipeline is null and sendToFailurePipeline returns immediately with no side effects

Issues Resolved

N/A

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed off