ACP-55692: document NFS CSI StorageClass domain switch

[Muyan0828]

Summary

• Add the English ACP KB solution for switching an NFS CSI StorageClass server domain while preserving the StorageClass and PVC names.
• Cover same-name StorageClass recreation, new PVC validation, per-PVC PV/PVC rebinding, Retain protection, rollback, and different-backend handling.
• Keep the procedure code-free and preserve the old NFS endpoint until migration and rollback windows close.

Validation

• Reproduced the forward flow on business-1 (ACP v1.34.5-8): same-name StorageClass recreation, new PVC provisioning, existing PVC rebinding, data read/write, and closeout.
• Reproduced PVC/PV rollback on the same test cluster.
• Test resources were cleaned from namespace acp-55692-nfs-test.
• Markdown structure and whitespace checks passed.
• yarn test:translation was not runnable in this checkout because the Yarn node_modules state file is absent; translation is generated by the repository workflow.