(gen2-migration): create an app for `imported` auth

[iliapolo]

We currently have code-generation support for imported auth located here:

https://github.com/aws-amplify/amplify-cli/blob/gen2-migration/packages/amplify-cli/src/commands/gen2-migration/generate/amplify/auth/reference-auth.generator.ts

However, we have not yet validated this works with a live integration test. This task is about making sure this use case works.

Ideally, it would result in a new migration app, but since this kind of app requires pre-existing resources, it requires enhancement to our e2e system to allow running a "pre-init" script. For now, lets just validate this manually and see where we take it from there.

• Gen1: https://docs.amplify.aws/gen1/javascript/build-a-backend/auth/set-up-auth/. switch to Amplify CLI (Import) tab.
• Gen2: https://docs.amplify.aws/react/build-a-backend/auth/use-existing-cognito-resources/#use-auth-resources-with-an-amplify-backend

[github-actions]

This issue is now closed. Comments on closed issues are hard for our team to see.
If you need more assistance, please open a new issue that references this one.