[Feature] Expose call metrics for the proxy admin gRPC interface #11474

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I checked open and closed issues and PRs for proxy admin metrics, OpenTelemetry on the control plane and admin gRPC instrumentation. What exists is adjacent, not this:

• [Bug] Proxy OTLP header parsing can reject valid values and expose secrets #10901 / Metrics labels and headers discard values containing colons #10833 touch how metric config values are parsed (OTLP headers, colon-separated labels); [Bug] Proxy and broker configuration logs may expose sensitive values #10950 masks them in config logs.
• [RIP-2] Add proxy admin online client query endpoint #10603 (RIP-2) adds its own ClientAdminMetricsRecorder for the new client-admin query endpoint — service-level instrumentation for code that does not exist on develop yet.
• Proxy Admin: standardized gRPC management interface on the Proxy #10825 tracks the admin interface work in general.

Nothing records anything for the admin gRPC server that actually ships today: ProxyAdminAuthInterceptor answers every admin RPC (thread dumps, message verification, group resets, topic updates...) and rocketmq_proxy_up is the only proxy instrument in the pipeline.

What happened?

ProxyMetricsManager initializes an OpenTelemetry meter in both proxy modes and exports it (OTLP/Prometheus/log), but the only instrument it registers is the rocketmq_proxy_up gauge. The admin gRPC server — the control plane surface every ops tool talks to — contributes no counter, no latency histogram, no error count.

So on a running proxy you cannot answer: is the admin interface being called at all, which methods are hot, how long do admin calls take, and — the important one — is anything failing (auth rejections, broken forwards, internal errors) while the dashboard still shows a healthy rocketmq_proxy_up = 1.

Expected behavior

Each admin RPC should produce one count and one latency sample, labeled with the method name and terminal status code, exported through the proxy's existing OpenTelemetry pipeline alongside rocketmq_proxy_up. Calls rejected by the auth interceptor should be counted too (that is where failures would show up first), and everything should degrade to a no-op when metrics are disabled or the manager has not started — same idiom the broker uses for optional instruments.

Runtime

develop at 57c2dc0, JDK 11. No proto change, no new dependency: the interceptor, the two instruments and tests live entirely in proxy.