feat(pod-group): add validation on subgroup names

[faizan-exe]

Description

This PR validates if the subGroup names are lowercase in admission webhook.

Related Issues

Fixes #948

Checklist

• [Yes] Self-reviewed
• [Yes] Added/updated tests (if needed)
• [Nil] Updated documentation (if needed)

Breaking Changes

No breaking changes.

[faizan-exe]

PTAL. Thanks!
cc - @itsomri

[itsomri]

Looks great!

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/NVIDIA/KAI-scheduler/pkg/apis/scheduling/v2alpha2	16.61% (+1.75%)	👍

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/NVIDIA/KAI-scheduler/pkg/apis/scheduling/v2alpha2/podgroup_webhook.go	63.89% (+2.35%)	72 (+7)	46 (+6)	26 (+1)	👍

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/NVIDIA/KAI-scheduler/pkg/apis/scheduling/v2alpha2/podgroup_webhook_test.go

[gshaibi]

Hi @faizan-exe , thanks for the contribution!

The validation logic looks correct, but I think we should use a +kubebuilder:validation:Pattern marker on the Name field (and Parent field) in podgroup_types.go instead of adding this in the webhook.

The field already uses kubebuilder markers (+kubebuilder:validation:MinLength=1), so adding a Pattern constraint would enforce this at the CRD/OpenAPI schema level by the API server itself — before the request ever reaches the webhook. This is more idiomatic for Kubernetes APIs and provides defense-in-depth.

The same pattern should also be added to the Parent *string field, since it references subgroup names.

The webhook should still keep the cross-field validations (duplicate names, parent existence, cycle detection), as those can't be expressed declaratively.

After the change, run make manifests to regenerate the CRD.