This is a clone of issue OCPBUGS-25462. The following is the description of the original issue:
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The number of control plane replicas defined in install-config.yaml (or agent-cluster-install.yaml) should be validated to check its set to 3, or 1 in the case of SNO. If set to another value the "create image" command should fail.

We recently had a case where the number of replicas was set to 2 and the installation failed. It would be good to catch this misconfiguration prior to the install.