test: add e2e test for OpenCensus to OpenTelemetry metrics migration

[khrm]

Verifies PR #9043's OTel migration by creating TaskRuns (success, fail, cancel, timed) and PipelineRuns (single-task, multi-task, cancel), then scraping the controller /metrics endpoint to assert counter values, histogram observation counts and bucket placement, gauge presence, metric renames (kn_workqueue_, go_), and removed metrics.

Changes

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[khrm]

/kind misc

[Copilot]

Pull request overview

Adds a new Go e2e integration test in ./test to validate the OpenCensus → OpenTelemetry metrics migration from PR #9043 by creating a representative set of TaskRuns/PipelineRuns and scraping the controller’s /metrics endpoint to assert expected metric presence/absence and basic value characteristics.

Changes:

• Introduces a consolidated e2e test that provisions successful/failed/cancelled/timed TaskRuns and several PipelineRun variants.
• Scrapes controller Prometheus metrics via the apiserver pod proxy and parses metric families for assertions.
• Adds checks for renamed infrastructure metrics (e.g., kn_workqueue_*, go_*) and confirms removal of legacy reconcile metrics.

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[khrm]

Somehow build is failing in CI. But locally everything works.

SYSTEM_NAMESPACE=tekton-pipelines go test -v -tags=e2e -count=1 -timeout=15m -run ^TestOTelMetrics$ ./test/

[khrm]

Somehow tests are failing with latest ko not the older version of ko.