Make Threeport labels consistent across custom resource types

[randalljohnson]

When Threeport manages Kubernetes objects on behalf of a user, it applies a standard set of labels to them which are useful when debugging in the Kubernetes API. These are currently only applied to Kubernetes-native object types, and not extensions of its APIs (custom resources). It would be nice if there were a way to support these. Additionally, some custom resources are used to configure operators which themselves are responsible for the management of an object. For example, a Postgres object that is consumed by the Zolando Postgres operator and manages an instance of Postgres. The created Postgres database will not have any labels applied to it to associate it with Threeport.