use operator domain as a valid service domain

Currently, the intent of the domains[] list is to allow the user to specify the domains a user will access that will hit the CDN edge nodes with the provider.

When using an operator domain (DNS driver), the customer currently has to CNAME their domain (matching above) to this operator domain.

Sometimes, it is useful to be able to hit the operator domain, and have it serve traffic from the edge. Depending on the provider (e.g. Fastly), this may mean that the operator domain needs to be configured as part of their service.

This spec is to allow that change to happen. Ie when an operator domain is created, create it as a domain at the provider to be able to also serve traffic from that origin. This should be configurable (on / off) and should apply to all provider drivers.