KIP-1223 — Add user tag to DeprecatedRequestsMetric

Discussion MetricsSecurity

Adds an optional user (principal name) tag to the DeprecatedRequestsPerSec JMX metric, gated behind a new config kafka.metrics.deprecated.requests.tag.user.enabled. The existing metric from KIP-896 could not identify which principal was sending deprecated API requests in multi-tenant clusters where multiple users share the same client.

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