Configmap for docker registry and notary server to be used.

[marcofranssen]

To be able to run the admin interface for multiple registries with their own notary sidecars or shared sidecars it should be possible to define a map of registry and related notary server.

e.g.

repos starting with docker.io should use notary.docker.io
repos starting with myregistry.com should use notary.internal.company.com
etc.

This also means more advanced authentication mechanism needs to be put in place #48.

[marcofranssen]

https://github.com/docker/cli/blob/2291f610ae73533e6e0749d4ef1e360149b1e46b/cli/trust/trust.go#L66-L79

Not configuring the Notary server might also be an option and have it resolve to the image domain. However this would require some kind of regex matching pattern on the target docker registry and sidecar to sent the traffic to either the registry or the notary server.