Organize CoreDNS and kube-proxy manifests so they're optional

[dghubble]

• Add components variable to configure CoreDNS and kube-proxy manifests. Allow provisioning clusters without CoreDNS or kube-proxy by disabling these components, so they can be customized or managed through separate plan/apply processes or automation

# default
components = {
  enable = true
  coredns = {
    enable = true
  }
  kube_proxy = {
    enable = true
  }
}