Setup automatic redirect from built-in fly.io domain to custom domain

[dindrick]

Add redirect so app is inaccessible via built-in fly domain. Right now app is still accessible via https://edgi-cloud.fly.dev/. Site should only be accessible from primary domain (for live this is https://resette.envirodatagov.org/)

Resources:
https://community.fly.io/t/disable-the-default-domain/11032/4