Replace the redirector app on GAE with nginx Cloud Run service

[upodroid]

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.

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[dprotaso]

/lifecycle frozen

[upodroid]

/transfer knative/infra