GitHub Sponsors: Fiscal host support for user accounts

Today, we're adding support for users to create a GitHub Sponsors profile and choose to receive sponsorship payouts via a fiscal host. This will give maintainers more flexibility and choice in how they receive funding. This has already been possible for organizations creating a GitHub Sponsors profile, and that remains unchanged. Users and organizations can still choose to use a Stripe Connect account instead of a fiscal host if they prefer. Learn more about signing up for a GitHub Sponsors profile using a fiscal host.