feat(metrics): Migration from OpenCensus to OpenTelemetry

[infernus01]

Changes

Migrates Triggers metrics implementation from the deprecated OpenCensus library to OpenTelemetry, aligning with Knative's observability stack modernization.

Changes include:

• Replace OpenCensus imports (go.opencensus.io/stats, stats/view, tag) with OpenTelemetry (go.opentelemetry.io/otel, otel/attribute, otel/metric) in pkg/sink/metrics.go and pkg/reconciler/metrics/metrics.go
• Convert elDuration to metric.Float64Histogram, eventRcdCount and triggeredResources to metric.Int64Counter
• Convert reconciler gauge metrics (eventlistener_count, triggerbinding_count, clustertriggerbinding_count,
  triggertemplate_count, clusterinterceptor_count) to metric.Float64Gauge
• Update knative.dev/pkg to v0.0.0-20260120122510-4a022ed9999a (includes new observability package)
• Update knative.dev/eventing to v0.0.0-20260209140146-9e76da08faaa (compatible with new knative.dev/pkg without deprecated metrics package)
• Update tektoncd/pipeline to v1.10.0 (OpenTelemetry migrated)
• Update test expectations for new observability config format (K_OBSERVABILITY_CONFIG replacing K_METRICS_CONFIG and K_TRACING_CONFIG)
• Simplify metrics tests to work without deprecated knative.dev/pkg/metrics/metricstest

All existing metrics continue to be exported with the same names and semantics. Counter metrics gain a _total suffix per Prometheus naming conventions when using the OTel Prometheus exporter.

fixes : #1964
/kind feature

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

Migrated metrics from OpenCensus to OpenTelemetry.

  ACTION REQUIRED:

  1. Configuration key change
     Replace metrics.backend-destination with metrics-protocol in your config-observability-triggers ConfigMap.
     Prometheus export remains the default — no change needed if you were not customizing observability.

  2. Infrastructure metric renaming
     Infrastructure metrics (workqueue, K8s client) have been renamed from the
     tekton_triggers_controller_ prefix to standard Knative/OpenTelemetry namespaces.

     ┌──────────────────────────────────────────────────────────┬───────────────────────────────────────────────────┐
     │ Old Metric Name (OpenCensus)                             │ New Metric Name (OpenTelemetry)                   │
     ├──────────────────────────────────────────────────────────┼───────────────────────────────────────────────────┤
     │ tekton_triggers_controller_workqueue_depth               │ kn_workqueue_depth                                │
     │ tekton_triggers_controller_workqueue_adds_total          │ kn_workqueue_adds_total                           │
     │ tekton_triggers_controller_workqueue_queue_latency_*     │ kn_workqueue_queue_duration_seconds_*             │
     │ tekton_triggers_controller_workqueue_work_duration_*     │ kn_workqueue_process_duration_seconds_*           │
     │ tekton_triggers_controller_workqueue_unfinished_work_*   │ kn_workqueue_unfinished_work_seconds              │
     │ tekton_triggers_controller_workqueue_retries_total       │ kn_workqueue_retries_total                        │
     │ tekton_triggers_controller_client_latency               │ http_client_request_duration_seconds_*            │
     │ tekton_triggers_controller_client_results               │ kn_k8s_client_http_response_status_code_total     │
     └──────────────────────────────────────────────────────────┴───────────────────────────────────────────────────┘

  3. Sink counter metrics renamed

     ┌──────────────────────────────────────────┬────────────────────────────────────────────┐
     │ Old Metric Name (OpenCensus)             │ New Metric Name (OpenTelemetry)            │
     ├──────────────────────────────────────────┼────────────────────────────────────────────┤
     │ eventlistener_event_received_count       │ eventlistener_event_received_total         │
     │ eventlistener_triggered_resources        │ eventlistener_triggered_resources_total    │
     └──────────────────────────────────────────┴────────────────────────────────────────────┘

  4. All other metric names are unchanged
     controller_eventlistener_count, controller_triggerbinding_count,
     controller_triggertemplate_count, controller_clustertriggerbinding_count,
     controller_clusterinterceptor_count, eventlistener_http_duration_seconds

[khrm]

Can you first run hack/update-codegen.sh ?

[khrm]

Please separate vendor and code changes into separate PR. It makes it easier to review.

[khrm]

Can you rebase this?

Also, ensure that generated related changes are there with vendor update commit.

[khrm]

Did you test the metrics? Can you write release note which mention any changes/breaking changes that user need to make?

[khrm]

Instead of having event_received_count_total, it's better to have event_received_total.

[infernus01]

Thanks @khrm for a thorough review!

[khrm]

I have updated the release note. Will merge soon.

[khrm]

/approve

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[khrm]

/lgtm