[AMQ7] StatefulSet templates should define a headless service for pod identity

The current AMQ 7 broker templates with StatefulSets don't define any headless service as a "serviceName" parameter of the StatefulSet

The headless service and the serviceName is important so that the pods gain a DNS resolvable name inside the cluster.

see https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#components

currently it is not possible to refer to the individual pods, so one cannot reasonably configure clients such as :

failover://(tcp://broker-amq-0.broker-amq.foo.svc.cluster.local:61616,tcp://broker-amq-1.broker-amq.foo.svc.cluster.local:61616)