KIP-608 — Expose Kafka Metrics in Authorizer

Accepted SecurityMetrics

Passes the broker's `Metrics` instance to authorizer plugins via a new `AuthorizerServerInfo` context object so authorizers can register and expose their own JMX metrics using the broker's existing metric infrastructure. Authorizer plugins previously had no access to the broker's metrics registry, forcing them to create their own `Metrics` objects with separate JMX reporters.

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