This commit updates the angular.io deployment script (`deploy-to-firebase.js`) to support deploying release-candidate versions. This is part of the work needed to prepare angular.io for our [new versioning/branching process][1] (also tracked in #39366). [1]: https://docs.google.com/document/d/197kVillDwx-RZtSVOBtPb4BBIAw0E9RT3q3v6DZkykU PR Close #39470