KIP-136 — Add Listener name to SelectorMetrics tags

Accepted Kafka 1.0 MetricsBroker

Adds listenerName and securityProtocol tags to the socket-server-metrics group so per-network-processor metrics (connection-count, connection-close-rate, etc.) can be filtered by listener. With multiple listeners on a broker, network processor IDs were bare integers, making it impossible to attribute socket-level metrics to a specific listener without knowing the processor-to-listener mapping.

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