Migrate scaling configuration to standard approach

[planetf1]

The current scaling (ie going from 1 replica to 3, of a platform) is modelled on the 'memcached' sample operator.

However a richer standard is now part of Kubernetes, so it would be more consistent to migrate the operator over to this approach:

See https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#scale-subresource