Restore defaultProviders.metrics in oauth2-proxy istio mesh config

[noisonnoiton]

✏️ Summary of Changes

The istio-external-auth-patches component replaces the entire istio mesh
config string in the istio ConfigMap (istio-system) to add the oauth2-proxy
extensionProviders. In doing so it dropped defaultProviders.metrics: [prometheus], which the base istio install ships
(common/istio/istio-install/base/install.yaml).

Without defaultProviders.metrics, istiod stops injecting the istio.stats
telemetry filter into the sidecar listeners. As a result istio_requests_total
is never produced, Prometheus scrapes empty telemetry, and Kiali traffic graphs
stay empty even though the mesh is healthy and serving traffic.
Istio standard telemetry metrics (including istio_requests_total) are no longer emitted.

This restores the three missing lines so the patched mesh config matches the
base install:

    defaultProviders:
      metrics:
      - prometheus

Verification:

kustomize build example \
  | yq 'select(.kind=="ConfigMap" and .metadata.name=="istio") | .data.mesh' \
  | grep -A2 defaultProviders

Before: no defaultProviders in the rendered istio ConfigMap.
After: defaultProviders.metrics: [prometheus] present alongside the
oauth2-proxy extensionProviders.

📦 Dependencies

None.

🐛 Related Issues

None. Straightforward regression fix restoring parity with the base istio
install configuration.

✅ Contributor Checklist

• I have tested these changes with kustomize. See Installation Prerequisites.
• All commits are signed-off to satisfy the DCO check.
• I have considered adding my company to the adopters page to support Kubeflow and help the community, since I expect help from the community for my issue (see 1. and 2.).

[github-actions]

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[Copilot]

Pull request overview

This pull request restores the missing defaultProviders.metrics: [prometheus] stanza in the Istio mesh configuration rendered by the istio-external-auth-patches component, ensuring that the oauth2-proxy extensionProviders patch remains aligned with the base Istio installation behavior and that telemetry metrics such as istio_requests_total are produced again.

Changes:

• Add back defaultProviders.metrics: - prometheus to the mesh configuration string in the patched istio ConfigMap.

[juliusvonkohout]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: juliusvonkohout

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• common/oauth2-proxy/OWNERS [juliusvonkohout]

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