With the ability to choose between the OpenShift Image Builder and a custom pod builder, it would be great if one could choose between the two manually. While most cluster admins may not want to use this knob, it would aid testing and debugging since it would allow an OpenShift developer or QE person to select which builder they're using. Additionally, when a cluster admin submits a must-gather, it would clearly show up and indicate which builder they are using.

There is a preexisting on-cluster-build-config ConfigMap that this key can belong to. So this work would primarily consist of reading this ConfigMap before starting the BuildController and determining which of the image builders should be used. A stretch goal would be to have the MCO restart the Machine OS Builder pod if this value should change, though I don't think this behavior is required for an MVP.

Done When:

• The on-cluster-build-config ConfigMap has a key for an imageBuilder value which can consist of either openshift-image-builder or custom-pod-builder.
• Some basic validation is done to determine that the imageBuilder value can be used.
• The Machine OS Builder startup process reads the on-cluster-build-config ConfigMap at startup and uses the desired imageBuilder.
• Stretch Goal: Make the Machine OS Builder pod restart if this value changes.