User Story

As a ROSA SRE, I would like to be able to use the Terraform-free Installer image ("altinfra") when deploying OpenShift on ROSA.

Engineering Details

Right now the release payload includes three (non-agent) installer images:

$ oc adm release info quay.io/openshift-release-dev/ocp-release:4.15.0-ec.1-x86_64 | grep installer | grep -v agent
  baremetal-installer                            sha256:96a38c2e8c5ea7826fe7bc0dcdccd5a8a4d6bfdc5c902e14d188944a92a8d784
  installer                                      sha256:82b167030e3960029cae599775b83803d9f7f17f5a162e5f6c1a460d9a44a4ce
  installer-artifacts                            sha256:835f0b56c520240fde7e17142f03ce32d820b56a752436bb58f85218562129bb

 
CORS-2876 will include an additional image, tentatively called installer-altinfra, in the release payload. ROSA will need to be able to use this image to have a terraform-free install path.

One potential method for enabling this would be to enable obtaining the altinfra image by using an `installer-altinfra` tag similiar to this code: https://github.com/openshift/hive/blob/3c31b4d7a61919ee62daf4eca4fc53951226b06d/pkg/imageset/updateinstaller.go#L170

Another alternative which is already implemented, would be to use the installerImageOverride, but it is unclear at this time if this would be acceptable to the ROSA client.