Add staged Enterprise Wiki migration cmdlets

[TaoziZ03]

Type

• Bug Fix
• New Feature
• Sample

Related Issues?

Cross-repository dependency: pnp/pnpframework#1278.

What is in this Pull Request ?

Adds a three-stage Enterprise Wiki migration workflow:

• Export-PnPEnterpriseWikiPackage captures a source-only, digest-sealed snapshot and does not require a target connection.
• New-PnPEnterpriseWikiMigrationPlan probes the target, produces explicit field/dependency decisions, and writes a complete Markdown review report.
• Import-PnPEnterpriseWikiMigrationPackage accepts the plan result through the pipeline, validates the approved digest, repeats preflight, and executes only sealed actions.

Every Pages-library field is retained in the source snapshot. The importer writes only recognized, writable, type-compatible fields; unknown values remain EvidenceOnly, while user, lookup, and taxonomy values remain RequiresMapping until a reviewed mapper exists.

Lifecycle is derived from source evidence rather than a publish switch: only an unambiguous Published source is published, and every other state is imported as Draft. The public Publish/Draft input is removed. Force only controls local artifact overwrite.

Validation

• solution built successfully against the Framework changes in Add staged publishing-page migration framework for Enterprise Wiki pnpframework#1278 using PnPFrameworkPath
• reflected cmdlet surface contains exactly the three new Enterprise Wiki commands
• pipeline binding, parameter sets, aliases, output types, and docs were checked for drift
• full three-stage pipeline metadata was validated

This is intentionally a Draft PR while the Framework dependency and tenant-backed acceptance run are reviewed. No live tenant import was performed while preparing the PR.