#352 adds gateway owning labels. These labels are applied to the Envoy service and reference the gateway ns/name used to create the service. The Kube provider gateway controller watches services and reconciles the correct gateway, e.g. update gateway.status.addresses when the Envoy service is assigned a load-balancer IP. Labels were chosen instead of annotations based on guidance from the Kubernetes Annotations/Labels docs:

Labels can be used to select objects and to find collections of objects that satisfy certain conditions. In contrast, annotations are not used to identify and select objects. The metadata in an annotation can be small or large, structured or unstructured, and can include characters not permitted by labels.

Should we proceed with Labels or Annotations to solve this problem?