KEP-6063: Update README to match Alpha implementation

[BhargaviGudi]

What this PR does / why we need it

Updates the KEP-6063 README to align with the Alpha implementation in kubernetes/kubernetes#139277.

Changes

• Resource name: pid → pids throughout (API field, YAML examples, user stories, validation rules, tests, dependencies, drawbacks)
• Metric deferred: Removed kubelet_pod_pid_limit_applied_total from Alpha graduation criteria, monitoring, and SLI sections; noted as deferred to Beta in "missing metrics"
• New dependency: Added PodLevelResourcesFixKubeletQOSClass (Beta, enabled by default since v1.37) to Feature Gate and Dependencies sections
• NDF declaration decoupled from cgroupsv2: Discover() only checks the feature gate; cgroupsv1 incompatibility is handled by kubelet admission
• Kubelet gate-off behavior: Kubelet rejects pods during admission when gate is off, not silently falls back to node default
• Version skew: Updated all scenarios to reflect fail-closed kubelet admission
• Validation ratcheting: Apiserver uses validation rejection + ratcheting for existing pods, not field stripping
• Enforcement function: min() capping logic lives in EnsureExists, not getPodPIDLimit
• Eviction e2e tests: Removed 4 eviction e2e scenarios (coverage moved to unit tests)
• Minor cleanup: Removed misleading intro line in Valid Values section

Related PRs

• Enhancement: Configuration for Per-Pod PID Limit #6063
• KEP: KEP-6063: Configuration for Per-Pod PID Limit #6064
• Implementation: KEP-6063: Support per-pod PID limits via resources.limits.pids (Alpha) kubernetes#139277
• Min PID limit update (separate): KEP-6063: Update minimum per-pod PID limit from 1024 to 128 #6217

/sig node
/cc @haircommander @ngopalak-redhat

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[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: BhargaviGudi
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[BhargaviGudi]

@SergeyKanzhelev @haircommander @mrunalp

This updates the KEP README to reflect the current Alpha implementation in kubernetes/kubernetes#139277:

• Resource name is pids (plural), not pid
• Removed kubelet_pod_pid_limit_applied_total metric (deferred past Alpha per review feedback)
• Added PodLevelResourcesFixKubeletQOSClass as a required dependency

No functional changes; just aligning the KEP with implementation.
Could you please help to review and approve the PR? Thanks

[harche]

/assign

[harche]

Thanks for updating the KEP to match the implementation. One spot I could not attach an inline comment to because the line is outside the diff: the Risks item "Version skew: apiserver accepts but kubelet ignores" has the same outdated assumption as my comment on the Feature Gate section, with the fail closed admission the kubelet rejects the pod rather than silently applying the node default: https://github.com/kubernetes/kubernetes/blob/f050421a6693073df402fde0cc9f3568087c2d1e/pkg/kubelet/lifecycle/features_linux.go#L62-L70

[harche]

/ok-to-test

[BhargaviGudi]

/test pull-enhancements-test

[harche]

LGTM.

/hold until kubernetes/kubernetes#139277 merges, so that we can accommodate more amendments, should we need any more.