The e2e testing suite should inject a more suitable namespace label

[timflannagan]

We currently inject a name: <namespace_prefix>-metering-testing-ns label for all of the namespaces that get created as a run of a single e2e instance, where <namespace_prefix> is either a user-provided go test flag, or derived from the METERING_NAMESPACE environment variable value. We do this for tenancy reasons to avoid stomping on other e2e runs instantiated by different users.

The problem is the name key is a relatively common key that is used in labels, so we should transition to something more distinct to avoid any further collisions.