Documentation: broken link in get-started guide

[dogezen]

The Ash Authentication getting started page https://hexdocs.pm/ash_authentication/get-started.html has a link Integrating Ash Authentication and Phoenix that is currently broken: https://hexdocs.pm/ash_authentication_phoenix/getting-started-with-ash-authentication-phoenix.html

[zachdaniel]

Fixed with a redirect in ash_authentication_phoenix's docs.