Add istio virtualservice to katib external-db

[namejsjeongkr]

What this PR does / why we need it:

Summary

Adds ui-virtual-service.yaml to enable automatic /katib/ UI routing for users deploying Katib with external databases.

Before: Users had to manually create Istio VirtualService after kustomize build manifests/v1beta1/installs/katib-external-db.
After: kustomize build automatically includes Istio integration

Motivation

Users of katib-external-db must manually create VirtualService. This cherry-picks katib-with-kubeflow/ui-virtual-service.yaml.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[github-actions]

🎉 Welcome to the Kubeflow Katib repo! 🎉

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Next steps:

• Our team will review your PR soon! cc @kubeflow/wg-automl-leads
• Check out the Contributing Guide and the Kubeflow Contributor Guide
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Feel free to ask questions in the comments. Thanks again for contributing! 🙏

[google-oss-prow]

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[juliusvonkohout]

@andreyvelich for approval and review.

[namejsjeongkr]

@Electronic-Waste @gaocegege @johnugeorge Is there any someone can review and approve ?

[andreyvelich]

Why do we need it here if Katib already has virtualService for Kubeflow Platform installation: https://github.com/namejsjeongkr/katib/blob/63f4611b27912222636057fd3c70b8e3ffa3c37c/manifests/v1beta1/installs/katib-with-kubeflow/ui-virtual-service.yaml ?

[namejsjeongkr]

@andreyvelich Thank you for the review!

You're right:

• katib-with-kubeflow: Full Kubeflow platform (embedded manifests) VS included
• katib-external-db: Standalone Katib + external PostgreSQL (custom MLOps) Missing VS

Real issue:
kustomize build katib-external-db | kubectl apply -f -
→ katib-ui pod healthy, but dashboard shows "Sorry, /katib/ is not a valid page"

This PR: Cherry-picks identical VS from katib-with-kubeflow → one-command Istio for standalone users.

[namejsjeongkr]

@andreyvelich I'm looking for your reply