KEP-5073: Add DV-only implementation details and update stability levels

[lalitc375]

• One-line PR description: This PR updates KEP-5073 to include details about the implementation of DV-only validation and to introduce stability levels for validation tags.
• Issue link: https://github.com/kubernetes/enhancements/issues/5073
• Other comments:
  • This change introduces the following to KEP-5073:
    • Tag Stability Levels: Defines Alpha, Beta, and Stable stability levels for declarative validation tags, with clear definitions and guarantees for each level.
    • DV-Only Implementation Strategy: Outlines the strategy for adopting DV-only validations. No DV-Only usage will be permitted in v1.35, which will instead focus on gathering metrics.
    • +k8s:declarativeValidationNative tag: Adds a new field-level tag to assert that a field's validation is handled exclusively by other stable +k8s: validation tags. The validation-gen tool will enforce that only stable tags are used with this marker and will fail if a field with this tag uses an Alpha or Beta validation tag.
    • Graduation Criteria: Updates the graduation criteria for tags to be promoted from one stability level to the next.

[lalitc375]

/assign @aaron-prindle @jpbetz

[jpbetz]

/approve
/lgtm

Thanks for nailing down the tag stability level details!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jpbetz, lalitc375

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