[AIT-73302] Align Immutable Infrastructure upgrade guidance for ACP 4.4

[chinameok]

Summary

• Make ACP product documentation the single owner of Phase 1 prerequisites, supported ACP Core paths, artifact preparation, and CVO procedures.
• Define Phase 2 as the provider-specific Kubernetes and Alauda OS replacement workflow using patch-specific OS Support Matrix rows.
• Centralize Kube-OVN upgrade and stage-1 recovery in one provider-version-aware procedure instead of duplicating mutable behavior across provider and global pages.
• Require provider upgrades before Kube-OVN chart v4.4+: DCS v1.0.22+, HCS v1.0.4+, VMware vSphere v1.0.16+, and Bare Metal v0.0.1+.
• Retain the legacy pre-v4.4 flows for older DCS, HCS, and vSphere providers; Bare Metal starts with the single official v0.0.1+ flow.
• Document the conditional Bare Metal global YAML workflow, normalize provider upgrade page titles, and correct the vSphere image delivery format to ova.
• Explain the Kubernetes 1.35 NeverVerify behavior without adding ACP-specific design rationale.

Kube-OVN source boundary

• Chart versions earlier than v4.4 use acp/chart-cpaas-kube-ovn.
• Chart v4.4 and later uses acp/chart-kube-ovn.
• New providers reconcile the complete AppRelease source and specification.
• Old DCS/HCS providers retain the annotation plus direct revision patch only for pre-v4.4 targets.
• Old vSphere providers retain annotation-only reconciliation for pre-v4.4 targets.
• A manual Kube-OVN-only source patch is not documented as a substitute for upgrading an old provider to ACP 4.4 behavior.

Recovery boundary

• Before a target-version control-plane Machine is created, restore Kube-OVN according to the installed provider version and restore the previous manifests.
• Same-minor OS or machine-template changes can be recovered through another replacement rollout where the provider supports it.
• After a target-minor control-plane Machine joins, use forward recovery or verified backup or DR restore; the documentation does not claim direct Kubernetes, CoreDNS, or etcd downgrade support.

Exclusions

• No ACP 4.4 OS Support Matrix row is added before formal release artifacts are available; AIT-70622 tracks that release-time update.
• No Release Notes changes are included.
• Bare Metal procedures require provider v0.0.1+ and a target OS Support Matrix row to be present in the installed release; the text does not claim availability before those release artifacts exist.

Validation

• git diff --check
• yarn lint — 0 errors, 0 warnings
• yarn build — passed; only the existing import.meta.env.SSR DefinePlugin warnings remain
• Targeted full-text checks for stale unconditional Kube-OVN patches, legacy chart-name claims, Bare Metal planned/pre-release wording, vmdk, and inconsistent provider page titles

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