add IPv6 to cluster-dns Usage Docs #9021

Job	Run time
build / Build	7m 15s
Integration Tests (certrotation)	1m 29s
Integration Tests (cacertrotation)	1m 18s
Integration Tests (etcdrestore)	1m 24s
Integration Tests (localstorage)	1m 8s
Integration Tests (startup)	6m 7s
Integration Tests (custometcdargs)	38s
Integration Tests (etcdsnapshot)	7m 15s
Integration Tests (kubeflags)	6m 22s
Integration Tests (longhorn)	2m 27s
Integration Tests (secretsencryption)	1m 46s
Integration Tests (flannelnone)	1m 2s
	38m 11s

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