Migrate metrics from OpenCensus to OpenTelemetry

[infernus01]

Changes

Migrates Operator metrics from the deprecated OpenCensus library to OpenTelemetry.

• Replace OpenCensus imports (go.opencensus.io/stats, stats/view, tag) with OpenTelemetry (go.opentelemetry.io/otel, otel/attribute, otel/metric) in tektonpipeline/metrics.go, tektontrigger/metrics.go, tektonchain/metrics.go, and tektonresult/metrics.go
• Convert counter metrics to metric.Int64Counter and gauge metric to metric.Float64Gauge
• Rewrite tektonresult/metrics_test.go to use sdkmetric.ManualReader for asserting actual collected metric values
• Update config-observability.yaml to use OTel configuration keys (metrics-protocol, tracing-protocol) and remove legacy OpenCensus keys
• Bump knative.dev/pkg to v0.0.0-20260318013857-98d5a706d4fd (OTel observability stack)
• Regenerate client code via ./hack/update-codegen.sh
  /kind feature

closes : #3307
fixes : #3331

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Release Notes

Migrated operator metrics from OpenCensus to OpenTelemetry.

ACTION REQUIRED:

1. Configuration key change
   Replace metrics.backend-destination with metrics-protocol in your tekton-config-observability ConfigMap.

2. Infrastructure metric renaming

   ┌──────────────────────────────────────────────────────────────────┬────────────────────────────────────────────────────┐
   │ Old Metric Name (OpenCensus)                                     │ New Metric Name (OpenTelemetry)                    │
   ├──────────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────┤
   │ tekton_operator_lifecycle_workqueue_adds_total                   │ kn_workqueue_adds_total                            │
   │ tekton_operator_lifecycle_workqueue_depth                        │ kn_workqueue_depth                                 │
   │ tekton_operator_lifecycle_workqueue_queue_latency_seconds        │ kn_workqueue_queue_duration_seconds                │
   │ tekton_operator_lifecycle_workqueue_work_duration_seconds        │ kn_workqueue_process_duration_seconds              │
   │ tekton_operator_lifecycle_workqueue_unfinished_work_seconds      │ kn_workqueue_unfinished_work_seconds               │
   │ tekton_operator_lifecycle_client_latency                         │ http_client_request_duration_seconds               │
   │ tekton_operator_lifecycle_client_results                         │ kn_k8s_client_http_response_status_code_total      │
   │ tekton_operator_lifecycle_go_*                                   │ go_*                                               │
   │ tekton_operator_lifecycle_reconcile_count                        │ removed (use kn_workqueue_adds_total)              │
   │ tekton_operator_lifecycle_reconcile_latency                      │ removed (use kn_workqueue_process_duration_seconds)│
   └──────────────────────────────────────────────────────────────────┴────────────────────────────────────────────────────┘

3. The following operator specific metrics are removed in this version since they were unused and not serving the purpose as expected. New metrics would be added as required in future work:

tekton_operator_pipeline_reconcile_count	
tekton_operator_trigger_reconcile_count
tekton_operator_chains_reconciled
tekton_operator_results_reconciled

[khrm]

I think we should remove metrics in the operator. These aren't used by customers or users. It was for some telemetry, but it's not working properly for that also.

If I get time, I would write more on that.

[jkhelil]

I think we should remove metrics in the operator. These aren't used by customers or users. It was for some telemetry, but it's not working properly for that also.

If I get time, I would write more on that.

We have stories to enhance overall metrics on operator, to move to olm level 3 and for 4, i didnt dig into details for these levels, but lets not remove metrics for now, until we tackle properly those stories please

[jkhelil]

@khrm would like to move forward with this, do you lgtm , or do you still think we need antoher approch removing metrics in operator ?

[infernus01]

@khrm For now I have updated the release notes sectino to not include those custom metrics.
Do you want me to remove those metrics from operator in this PR, or we can raise a follow-up issue to do so?

[jkhelil]

@khrm understood now, @infernus01 would you be able to update the PR then, i think it make sense to remove those to start with clean metrics list

[anithapriyanatarajan]

@infernus01 Please consider metioning the metrics that were removed as part of release notes. Also remove the metrics.go file if no metrics are recorded.

[infernus01]

@infernus01 Please consider metioning the metrics that were removed as part of release notes. Also remove the metrics.go file if no metrics are recorded.

Wouldn't that conflict with @khrm's comment, that it was not even documented before why we should even write that in release notes.?

[jkhelil]

/approve

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[anithapriyanatarajan]

@jkhelil @infernus01 - Under final review and verification. Will update here shortly. Thank you

[anithapriyanatarajan]

/ok-to-test

[anithapriyanatarajan]

/ok-to-test

[anithapriyanatarajan]

/lgtm