Add per-database throughput attribution metrics to EventProducer

[akshayrai]

Summary

• Adds bytesProducedRate and eventProduceRate metrics keyed by source database (EventProducer.db.<databaseName>.*) to EventProducer. These metrics are emitted on successful Kafka ack, gated by the enableThroughputAttributionMetrics config flag (default off).
• Covers CDC connectors automatically via URI parsing. No connector-specific changes needed. BMM pipelines (kafka://) emit no database metric since there is no source database concept.
• Aggregate and per-connector-type meters are also emitted for rollups.

Testing Done

• Includes unit tests