Replace the redirector app on GAE with nginx Cloud Run service

We inherited this app knative/test-infra#3250 from Google that redirects various *.knative.dev addresses.

This is currently deployed on app engine which isn't that easy to deploy against and requires manual changes. I would like to deploy this on to cloudrun with nginx.

Start by reviewing knative/test-infra#3250 and the existing App Engine deployment for the redirector app. Identify where the *.knative.dev redirects are configured, then determine the Cloud Run and nginx deployment requirements; done means the redirects work from the new service without manual App Engine changes.

Written by the indexing model from the issue text.