fix: validate LowNodeUtilization metrics source

[immanuwell]

Description

Tiny config validation fix, nothing fancy.

LowNodeUtilization accepted metricsUtilization: {} or a typo'd metricsUtilization.source. That can come straight from policy YAML, since source is just a string; no cloud quota / API ceiling blocks it. Later the plugin trips at runtime with metrics source is empty or unrecognized metrics source.

This catches that during policy validation instead. Legacy metricsServer: true stays valid.

Reproduce

Before the fix, the new table cases returned nil:

go test ./pkg/framework/plugins/nodeutilization -run TestValidateLowNodeUtilizationPluginConfig -count=1

Now they pass, and the wider package suite is clean:

go test ./pkg/...

Related search: #1658 and #1840 are in the same metrics config area, but this does not directly close them.

Checklist

• Code Readability
• Naming Conventions
• Code Duplication
• Function/Method Size
• Comments & Documentation
• Error Handling
• Testing
• Performance
• Dependencies
• Logging & Monitoring
• Backward Compatibility
• Resource Management
• PR Description
• Documentation & Changelog

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[a7i]

/ok-to-test

[k8s-ci-robot]

@immanuwell: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-descheduler-test-e2e-k8s-master-1-36	d4e0533	link	true	/test pull-descheduler-test-e2e-k8s-master-1-36

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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