chore: bump controller-runtime to v0.23.3 and migrate DiscoveredCluster webhook

[manusa]

Description

Moves the DiscoveredCluster webhook to the typed admission API so controller-runtime can be upgraded again.

discovery is still on controller-runtime v0.19.4. The Konflux bumps to v0.23/v0.24 (#1582, #1912, #2056, #2201) couldn't merge because api/v1/discovery_webhook.go uses webhook.Defaulter/webhook.Validator (removed in v0.20) and the untyped ctrl.NewWebhookManagedBy(mgr).For(r) builder (replaced in v0.23).

It also affects consumers of the API package: anything importing github.com/stolostron/discovery/api/v1 with controller-runtime >= v0.20 fails to compile. In fabric8io/kubernetes-client it's the last thing keeping our model generator off the Kubernetes 1.37 libraries.

The approach is the same as stolostron/backplane-operator#3153.

Related Issue

None filed, context above.

Changes Made

• controller-runtime v0.19.4 → v0.23.3, which matches the k8s.io v0.35 libraries already in use
• DiscoveredCluster webhook uses builder.WebhookManagedBy(mgr, r) with typed admission.Defaulter/admission.Validator; validation logic is unchanged
• Unit tests for Default, ValidateCreate, ValidateUpdate and ValidateDelete
• setup-envtest release-0.17 → release-0.23 and ENVTEST_K8S_VERSION 1.25 → 1.35.0; dropped --use-deprecated-gcs, which release-0.23 no longer accepts
• zz_generated.deepcopy.go as regenerated by make generate

Checklist

• I have tested the changes locally: make test (including the envtest controllers suite), go vet ./..., make generate manifests
• I have added/updated relevant unit tests (if applicable).

Additional Notes

With this change api/v1 also builds against controller-runtime v0.25.1 and k8s.io v0.37.0, which downstream consumers such as fabric8io/kubernetes-client need.

Reviewers

/cc @dislbenn

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This pull-request has been approved by: manusa
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[openshift-ci]

Hi @manusa. Thanks for your PR.

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