KIP-143 — Controller Health Metrics

Accepted Kafka 1.0 MetricsBroker

KIP-143 adds controller health metrics including `ActiveControllerCount`, `EventQueueSize`, `EventQueueTimeMs`, and `ControllerState` to detect slow progress or deadlocks in the Kafka controller. Existing controller metrics are insufficient to distinguish a healthy controller from one that is alive but making no progress on the event queue.

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