Add spec property to differentiate management and workload clusters

[mdsgabriel]

See #94

What would you like to be added:
Add a new property to cluster spec that will be used to identity if a cluster has management controllers

type ClusterSpec struct {
   ...
    Management                    *bool                          json:"management,omitempty"
}

Why is this needed:
CLI, controllers and webhooks will execute different code paths based on this property

[mdsgabriel]

closing this -- #429