How to make masters/control-plane schedulable during agent-based installation

Issue

During installation with the agent-based installer, control plane nodes are automatically made schedulable in the single-node and compact (<2 workers) topologies. However, for high-availability clusters (i.e. clusters with two or more worker nodes) the default is that user workloads cannot be scheduled to the control plane nodes.

When doing a UPI or IPI install, the scheduler manifest can be edited prior to creating the cluster. This is not possible with the agent-based installer.