What kind of change does this PR introduce?

broke it down into 4 scripts or "apps"
trigger-nix-build: this one will run and monitor the initial nix build so that your current commit on your branch will get cached. Runs the workflow remotely monitors on your machine.
aws-vault exec supabase-dev -- nix run .#build-test-ami 15 will build the AMI for testing, and give you the AMI id if successful, based on your current branch commit. This will clean up the ec2 instances used to do the build when it's done.
A nix app that will run the testinfra tests against the AMI id you pass it from the previous build. This way you can build the AMI once, and test it many times, since AMI build is time consuming. You can rebuild AMI if needed with. This will also clean up it's ec2 instance
A nix app that will deregister the testing AMI when you are done testing.