This interface allows a DNS provider, such as CoreDNS, to provide name resolution for a Kubernetes cluster.
(Note: this interface was previously used by the Kubernetes Master charm to
communicate the DNS provider info to the Kubernetes Worker charm, but that
usage was folded into the kube-control interface.)
The provider should look for the {endpoint_name}.connected flag and call
the set_dns_info method with the domain, sdn_ip, and port info (note:
these must be provided as keyword arguments).
The requirer should look for the {endpoint_name}.available flag and call the
details method, which will return a dictionary with the domain, sdn-ip,
and port keys.