Service exposition with ListenerClasses

The operator deploys a Listener for OpenSearch role-groups. The listener defaults to only being accessible from within the Kubernetes cluster, but this can be changed by setting .spec.nodes.roleGroups.{role-group-name}.config.listenerClass:

spec:
  nodes:
    roleGroups:
      cluster-manager:
        config:
          listenerClass: external-stable  (1)

1	Specify a ListenerClass, such as `external-stable`, `external-unstable`, or `cluster-internal` (the default setting is `cluster-internal`) at role-group level. This can be set for all role-groups individually.