With this change, Compute nodes within each MachineSet are automatically
created in a Server group, with a default policy of
"soft-anti-affinity".
With this change, a "serverGroupPolicy" can be set in install-config, on
the worker MachinePool and/or in the platform default.
Implements OSASINFRA-2570
Co-Authored-By: Matthew Booth <mbooth@redhat.com>