Added in NVA Changes for ILB Migration in Powershell

[Jordang3177]

Description

Adds PowerShell support for the Network Virtual Appliance (NVA) migration workflow, introduced in the Network API version 2025-09-01. This enables migrating an NVA to a new OS version or to the new internal load balancer (ILB) architecture.

New cmdlets (each supports both the resource-name and resource-id parameter sets and returns the updated PSNetworkVirtualAppliance):

• Invoke-AzNetworkVirtualAppliancePrepareMigration — stages the migration (-MigrationType MigrateToNewOSVersion | MigrateToNewILBArchitecture, optional -MarketPlaceVersion)
• Invoke-AzNetworkVirtualApplianceExecuteMigration — performs the prepared migration
• Invoke-AzNetworkVirtualApplianceCommitMigration — finalizes the migration
• Invoke-AzNetworkVirtualApplianceAbortMigration — rolls back an in-progress migration

Also adds a read-only MigrationStatus property (MigrationType / MigrationPhase / MigrationPhaseStatus) to the NVA output surfaced by Get-AzNetworkVirtualAppliance.

Includes the supporting SDK models/operations, AutoMapper mappings, markdown help, and scenario tests (Test-NetworkVirtualApplianceIlbMigration, -MigrationAbort, -MigrationByResourceId).

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • General release
  • Public preview
  • Private preview
  • Engineering build
  • No need for a release

• Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

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