KIP-196 — Add metrics to Kafka Connect framework

Accepted Kafka 1.0 ConnectMetrics

Adds comprehensive JMX metrics to Kafka Connect covering connector state, task state, worker utilization, source record rates, sink record rates, and error rates at the worker, connector, and task level. The existing Connect metrics were limited to counts of connectors and tasks per worker, providing no actionable data for monitoring SLAs, detecting failures, or capacity planning.

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