Enterprise Live Migrations: Moving from Azure DevOps Repo to GitHub with minimal disruption

Introduces Enterprise Live Migrations (ELM) for migrating repositories from Azure Repos to GitHub Enterprise Cloud with minimal disruption. ELM supports continuous synchronization of changes while development continues, followed by a brief cutover window (typically under 30 minutes), avoiding extended downtime. It begins with a validation step, followed by continuous sync, and concludes with a final cutover. Currently in limited public preview, with script-based migration available and a UI-based experience coming soon.