REST API endpoints for Visual Studio Subscription management

GitHub Enterprise Cloud admins can now use the following REST API endpoints to programmatically manage Visual Studio Subscription (VSS) assignments:

• GET /enterprises/{enterprise}/visual-studio-subscriptions: Returns all VSS assignments for an enterprise, including whether each assignment has been matched to a GitHub user.
• PUT /enterprises/{enterprise}/visual-studio-subscriptions: Maps a VSS UPN to a GitHub handle, enabling bulk programmatic matching.
• DELETE /enterprises/{enterprise}/visual-studio-subscriptions/{visual_studio_subscription_id}: Removes a manual match between a Visual Studio subscription and a GitHub user, allowing admins to correct mistaken assignments or programmatically rematch subscriptions.

These endpoints are especially useful for organizations where VSS UPN formats do not align with SCIM identities, a scenario that prevents automatic matching and previously required tedious manual resolution in the UI. Admins can now supply a UPN-to-GitHub-handle crosswalk and script bulk-matching operations.