feat: add helm lint and helm unit tests to CI

[Goku2099]

What this PR does

Adds a CI check using kube-linter to validate Kubernetes manifests and Helm charts.

This helps catch common configuration issues early and improves production readiness and security for Kubeflow deployments.

References:

• Issue Add CI pipeline to validate manifests and helm chart with kube-linter #3096
• Related work in feat: Add CI pipeline to validate manifests and helm chart #3101

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Details

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[coveralls]

Pull Request Test Coverage Report for Build 21621465317

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 51.217%

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Totals
Change from base Build 21610377640:	0.0%
Covered Lines:	1241
Relevant Lines:	2423

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💛 - Coveralls