Docker registry authentication

[devnatan]

We currently do not support authentication against the Docker registry, so private registries will not work. I was thinking of a simple implementation but nothing too concrete like this:

Yoki(Docker) {
    registry { // this: DockerRegistryAuthentication
        url = ""
        username = "johndoe"
        password = "yoki"
        email = "[email protected]"
    }
}

It should also be possible to get the authentication directly from the environment variables.