Add performance metrics to controllers

[Copilot]

Controllers lacked timing metrics for reconciliation operations.

New Prometheus histograms

• thundernetes_gameserver_reconcile_duration_seconds — GameServer controller reconcile latency
• thundernetes_gameserverbuild_reconcile_duration_seconds (BuildName) — GameServerBuild controller reconcile latency

All use prometheus.DefBuckets and register via promauto.With(metrics.Registry), consistent with existing metrics.

Instrumentation points

• GameServerReconciler.Reconcile — defer at method entry
• GameServerBuildReconciler.Reconcile — defer after fetching the GSB (so BuildName label is available)

Per-operation creation/deletion duration metrics were intentionally omitted since individual K8s API calls are very fast and those values would be close to zero. The reconciliation duration histograms already capture the full picture including all batch creation/deletion time.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add metrics to controllers </issue_title>
<issue_description>We should add performance metrics to controllers. Like how much time it took to reconcile, to create/delete X number of GameServers etc</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add metrics to controllers  #361

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[dgkanatsios]

@copilot the reconciliation metrics seem OK, but the creation/deletion metrics should be close to zero, as the call to K8s API server should be really fast. What do you think?

[Copilot]

@copilot the reconciliation metrics seem OK, but the creation/deletion metrics should be close to zero, as the call to K8s API server should be really fast. What do you think?

You're right — individual K8s API calls for creation/deletion are very fast, so those per-operation duration metrics would be near zero and not useful. Removed GameServerCreationDuration and GameServerDeletionDuration in 1e66795, keeping only the reconciliation duration histograms which already capture the full picture including all batch creation/deletion time.