Consul-helm: Docs need updating for CoreDNS

[nfisher]

Will try to make a PR but currently the docs relating to consul-helm here are related to kube-dns:

https://www.consul.io/docs/platform/k8s/dns.html

I believe as of k8s v1.11 CoreDNS is now the standard name server.

https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/#coredns

Unfortunately it's a completely different syntax for coredns vs kube-dns. :(

[madsonic]

i think this part in the docs is related as well. Perhaps stating the kubernetes version that needs to upgrade to CoreDNS would be helpful.

[nfisher]

Looks like GKE supports v1.11 but has kept kube-dns. Not sure what the other 1st tier cloud providers are doing?

[DWSR]

@nfisher CoreDNS is now GA and kube-dns has been deprecated per https://github.com/kubernetes/enhancements/issues/566 so it makes sense to update the documentation to at least add instructions for CoreDNS

[adilyse]

Adding CoreDNS instructions to the documentation in this Consul PR. Hopefully that helps clarify the situation for folks running CoreDNS now instead of kube-dns.

I'm going to close this, but please feel free to comment or open another issue if there is anything missing.