✨ Add support for k8s:enum tag.

[lalitc375]

This PR introduces support for a +k8s:enum marker to automatically generate enum validation for Custom Resource Definitions (CRDs). This tag is used by native types to validate enums using declarative Validations.

This change simplifies the process of defining enums in CRDs. Previously, developers had to manually specify all enum values using the +kubebuilder:validation:Enum marker for every field of an enum type. This was repetitive and prone to errors, especially when enum values changed.

With this new +k8s:enum type-level marker, controller-gen automatically discovers all constant values associated with a string-based enum type and generates the corresponding validation in the OpenAPI schema. This makes the process more maintainable and less error-prone.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @lalitc375. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[lalitc375]

Holding this PR, until we gets approval on DV.