ServiceType conflict resolution

[fredjywang]

In the case that a user is trying to export two services, one of ClusterIP and one of Headless, with the same namespaced name, the controller needs a way to reconcile the conflicting types.

Following the conflict resolution policy, this can be done by propagating the SeviceExport's creationTimestamp to Cloud Map Endpoints as a custom instance attribute, and the older service will take priority, with the newer service not getting exported to Cloud Map.