Set a custom production Git branch on Vercel

Introduced the ability to set a custom production Git branch for Vercel Projects. New projects will default to the 'main' branch (or 'master' if 'main' is absent) instead of the repository's default branch. A new Project Setting allows users to select 'main', the repository's default branch, or any other custom branch for production deployments. This change provides greater flexibility in managing deployment workflows.