istio: map Phase field to StopAfter checkpoints in pipeline runner

[trevorwilliams2025]

What

Map the IstioUpgradeStep.Phase field to internal StopAfter checkpoints in the pipeline runner.

Why

The Phase field (added in Azure/ARO-Tools#264) enables splitting Istio upgrades into discrete pipeline steps. This PR adds the consuming code that maps "install" to StopAfterCanaryStart (installs new control plane, stops before workload migration) and lets "upgrade" or empty run the full lifecycle. Splitting gives each phase its own EV2 timeout budget and allows a Helm config step to run between control plane installation and workload migration. The pipeline wiring (svc-pipeline.yaml) will follow in a subsequent PR.

Testing

The switch statement is a straightforward mapping with an error default. The StopAfter checkpoint logic is already covered by existing tests in tooling/templatize/pkg/istio/upgrade_test.go. Integration validation was performed manually against pers-dev.

Special notes for your reviewer

Depends on Azure/ARO-Tools#264 (Phase field).

PR Checklist

• PR is scoped to a single task (no mixed concerns)
• Title follows Conventional Commits format
• Summary explains the "Why" behind the change
• Linked to relevant ticket/issue
• Screenshots included (if graph/UI/metrics changes)
• Self-reviewed the diff
• CI/CD checks are passing (ignore Tide)
• Draft PR used for WIP (if applicable)
• Commit history is clean (rebased/squashed)
• Tricky code blocks are commented
• Specific reviewers tagged
• All comment threads resolved before merge

If E2E tests are included:

• E2E tests follow Principles of Good E2E Test Case Design
• If new E2E use case is covered (via a new test or new check/verifier),
  demonstrate that the test is able to detect a defect/error and fail with
  proper error message and logs which communicates nature of the problem.

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[Copilot]

Pull request overview

This PR updates the templatize pipeline runner’s Istio upgrade step handling to interpret the upstream types.IstioUpgradeStep.Phase field and translate it into internal Istio upgrade “stop-after” checkpoints, enabling split-phase upgrades (e.g., install control plane only vs full upgrade).

Changes:

• Map Phase=="install" to opts.StopAfter = istio.StopAfterCanaryStart.
• Treat Phase=="upgrade" or empty as “run full lifecycle” (no stop-after checkpoint).
• Reject unknown phase values with an explicit error.

[trevorwilliams2025]

/test images

[openshift-ci]

@trevorwilliams2025: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/verify	0594c20	link	true	/test verify
ci/prow/test-unit	0594c20	link	true	/test test-unit
ci/prow/e2e-images	094da0b	link	true	/test e2e-images
ci/prow/lint	094da0b	link	true	/test lint
ci/prow/periodic-healthcheck-images	094da0b	link	true	/test periodic-healthcheck-images
ci/prow/image-updater-images	094da0b	link	true	/test image-updater-images
ci/prow/config-change-detection	094da0b	link	true	/test config-change-detection
ci/prow/e2e-parallel	094da0b	link	true	/test e2e-parallel
ci/prow/images	094da0b	link	true	/test images

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