Extend Azure Repos migration with TFVC support

Overview

While we have this Epic to "incorporate" TFVC-git migration support in congregate, I believe it's beneficial provide runbook to our customers who are looking TFVC-git migration support. The purpose of this ticket is to come up with changes in our runbook for ADO and ADO matrix with detailed explanation (ideally with screenshots, pitfalls, caveats, planning, resources required for such migration). If any scripts are needed, we can keep them in here.

Tasks

• Update docs if needed (workflow, runbooks, README, migration metrics, etc.)

Acceptance Criteria

• Existing UTs pass locally
• 100% code coverage on new code

@gitlab-org/professional-services-automation/tools/migration