[Data Import] Migrate and re-map Active Directory group assignements

[NenoLoje]

Current state

Most companies use Active Directory groups to manage permissions to Azure DevOps Server these days.

As Migrator.exe does not check if these groups exist in Azure AD, the customer could end up with users not having permission to access Azure DevOps after the import, as the groups cannot be found in Azure AD.

Desired state

Migrator.exe prepare and Migrator.exe import should check if referenced groups do exist on Azure AD and re-map group assignment during import (similar to how users are mapped).