documentation: use server-side apply in README

[Denyme24]

Pull Request Template for Kubeflow Manifests

fixes #3325

✏️ Summary of Changes

Fixed the Spark Operator test script to use the correct kubeflow overlay instead of standalone, and added the --force-conflicts flag to resolve "metadata.annotations: Too long" errors during installation.

Changes:

• Updated overlay path from overlays/standalone to overlays/kubeflow in tests/spark_install.sh
• Added --force-conflicts flag to kubectl apply command to handle annotation size limits

📦 Dependencies

List any dependencies or related PRs (e.g., "Depends on #123").

🐛 Related Issues

Link any issues that are resolved or affected by this PR.

✅ 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.).

---

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[github-actions]

Welcome to the Kubeflow Manifests Repository

Thanks for opening your first PR. Your contribution means a lot to the Kubeflow community.

Before making more PRs:
Please ensure your PR follows our Contributing Guide.
Please also be aware that many components are synchronizes from upstream via the scripts in /scripts.
So in some cases you have to fix the problem in the upstream repositories first, but you can use a PR against kubeflow/manifests to test the platform integration.

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• CNCF Slack channels: https://www.kubeflow.org/docs/about/community/#kubeflow-slack-channels
• Community meetings: https://www.kubeflow.org/docs/about/community/

Thanks again for helping to improve Kubeflow.

[juliusvonkohout]

Thank you
/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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