Support for NodeExternalDNS

[arnemileswinter]

Is your feature request related to a problem? Please describe.
I am using Agones in my cluster and the GameServer resources can resolve their address to NodeExternalDNS as seen here:
https://github.com/googleforgames/agones/blob/02e57babccab6489b18d956286152174fe9a1eaa/pkg/gameservers/gameservers.go#L46

however, the entry on k3s is unpopulated - only NodeExternalIP can be resolved with the --node-external-ip flag when launching k3s server.

Describe the solution you'd like
A cli option like k3s server --node-external-dns example.com similar to --node-external-ip

Describe alternatives you've considered
I am currently using --node-external-ip and look up the server domains by comparing with that ip in a local configuration.

Additional context
It seems undocumented that NodeExternalDNS is a valid status entry on node types. I opened a PR there kubernetes/api#77 on k8s core v1 API Node Address type.

[brandond]

It's not undocumented, it is covered here : https://pkg.go.dev/k8s.io/api/core/v1#NodeAddressType

	// NodeInternalDNS identifies a DNS name which resolves to an IP address which has
	// the characteristics of a NodeInternalIP. The IP it resolves to may or may not
	// be a listed NodeInternalIP address.
	NodeInternalDNS [NodeAddressType](https://pkg.go.dev/k8s.io/api/core/v1#NodeAddressType) = "InternalDNS"

	// NodeExternalDNS identifies a DNS name which resolves to an IP address which has
	// the characteristics of a NodeExternalIP. The IP it resolves to may or may not
	// be a listed NodeExternalIP address.
	NodeExternalDNS [NodeAddressType](https://pkg.go.dev/k8s.io/api/core/v1#NodeAddressType) = "ExternalDNS"

We don't currently support setting either of the DNS types, just hostname and internal/external IPs.