pkg/registry/core/pod/storage: add PDB-specific CauseType to eviction forbidden errors

[shady0503]

What type of PR is this?

/kind feature
/kind api-change

What this PR does / why we need it:

When checkAndDecrement returns a Forbidden error due to negative DisruptionsAllowed or an oversized DisruptedPods map, clients had no programmatic way to distinguish these from other Forbidden errors without string-matching on the message.

This PR adds two new CauseType constants to policy/v1:

• DisruptionBudgetNegativeAllowedDisruptions — for the DisruptionsAllowed < 0 case
• DisruptionBudgetTooManyDisruptedPods — for the DisruptedPods map overflow case

And populates StatusCause on both Forbidden error paths in checkAndDecrement, consistent with the existing pattern already used on the TooManyRequests path via DisruptionBudgetCause.

Clients can now use errors.HasStatusCause(err, policyv1.DisruptionBudgetNegativeAllowedDisruptions) for reliable, typed, machine-readable error discrimination, no message parsing needed.

Which issue(s) this PR is related to:

Fixes #125500

Special notes:

The two new CauseType constants follow the same naming convention and placement as the existing DisruptionBudgetCause constant in staging/src/k8s.io/api/policy/v1/types.go. No codegen changes were required since CauseType is a string alias.

Does this PR introduce a user-facing change?

Added structured `CauseType` values to PodDisruptionBudget-related eviction `Forbidden` errors in the eviction API, allowing clients to programmatically distinguish PDB invalid-state errors from other forbidden errors without string-matching on the message.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: shady0503 / name: Chadi Taqi (507d980, 9d12121, f5882ac)

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[shady0503]

/easycla

[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[shady0503]

/label api-review

[soltysh]

/assign @tallclair
as a node approver

[shady0503]

@tallclair PTAL, this needs approval for pkg/registry/core/pod when you have a moment. CI is green.

[liggitt]

/lgtm
/approve

[shady0503]

/retest

[soltysh]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Details

Git tree hash: c89dee988b3d0fafe155b5f25167669543a5fda6

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: atombrella, liggitt, shady0503, soltysh

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Needs approval from an approver in each of these files:

• pkg/registry/core/pod/OWNERS [liggitt]

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