Add support for controller custom certificate in KnativeServing CRD #210

To enable the controller to trust self-signed certs from a registry, I'd like to propose the following addition to the KnativeServing CR:

spec:
  controller-custom-certs:
    name: config-service-ca
    type: ConfigMap

The operator would then configure the controller's deployment per these instructions. The other supported type would be Secret, both of which the user would be expected to create.