Add Vercel Analytics Umbraco package and sample app

[thebuilder]

Summary

• Adds the Umbraco.VercelAnalytics package with client-side dashboard, settings, section access, and API integration.
• Includes generated API clients, dashboard UI, supporting utilities, and targeted test coverage for analytics and settings behavior.
• Adds a runnable example Umbraco site plus updated docs, roadmap, and package metadata for the new integration.

Testing

• Unit tests added and updated for dashboard, breakdown, request coordination, URL state, settings, and helper logic.
• Sample app and client project wiring were validated at a high level during implementation.
• Not run (not requested)