chore: Add SHA256 verification for KinD and Kustomize installation

[christian-heusel]

Pull Request Template for Kubeflow Manifests

✏️ Summary of Changes

Describe the changes you have made, including any refactoring or feature additions.

Add SHA256 verification for KinD and Kustomize installation.

This guards us against the files being damaged in transport and is the
generally the right thing to do.

📦 Dependencies

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

None

🐛 Related Issues

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

None

✅ 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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[christian-heusel]

/retest

[juliusvonkohout]

Thank you
/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: juliusvonkohout

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