Currently there is an issue with redirecting `rc.angular.io` to
`angular.io` when there is no active RC. If a user has visited
`rc.angular.io` before and has a ServiceWorker registered for that
subdomain, they will never "see" the redirect to `angular.io`.
This commit fixes the problem by doing an additional deployment from the
stable branch to the `rc-angular-io-site` Firebase site when there is no
active RC. This additional deployment will ensure that:
1. Users will be temporarily redirected from `rc.angular.io` to
`angular.io`.
2. Users with a registered ServiceWorker (who don't see the redirect)
will have their ServiceWorker unregistered on the next visit.
3. The content on both sites is identical.
See #39760 for more details on the problem and the solution.
NOTE:
As mentioned in #39760, for this fix to take affect, we need to remove
the redirect from `rc.angular.io` to `angular.io` in the Firebase
console for site `rc-angular-io-site`.
Fixes#39760
PR Close#39853