Support default values for resources

[mastoj]

lt would be awesome if we could support something like:

let defaultK8sDeployment = deployment {
    ...
}

let k8sDeploy = deployment {
    withDefault defaultK8sDeployment
}

The k8s is just an example, we should be able to do that for everything. That will make it super easy to create small helpers that are reusable.