KIP-1301 — Deprecate Yammer-based metrics in `GroupCoordinatorMetrics`

Accepted Kafka 4.4 BrokerMetrics

Deprecates the remaining Yammer-based classic-group metrics in GroupCoordinatorMetrics (NumGroups, NumOffsets, NumGroupsPreparingRebalance/CompletingRebalance/Stable/Dead) and adds equivalent Kafka Metrics gauges under kafka.server:type=group-coordinator-metrics with protocol and state tags. The migration from Yammer Metrics to Kafka Metrics started in KAFKA-14519/KAFKA-15870 was left incomplete, so some group coordinator metrics were only reachable through Yammer while others were already on Kafka Metrics, leaving an inconsistent monitoring interface.

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