Use DNS without CoreDNS

[anjomro]

According to your docs (https://docs.netmaker.org/server-installation.html#no-dns-coredns-disabled) CoreDNS is not needed anymore for DNS since a hostsfile-based approach is used.

If I understand the docs correctly to use the new mode DNS_MODE needs to be set to on (or at least not to off), and CoreDNS can just be omitted from the setup.

However with this Helm-Chart this is not possible, since the value dns.enable is used for including or excluding the CoreDNS Service as well as setting the DNS_MODE to on if CoreDNS is included or off if CoreDNS is excluded.

How can we get DNS without using CoreDNS? Either an additional variable like dns.enable_coredns could be used to independently configure dns mode and CoreDNS or CoreDNS could be dropped entirely.

Either way I could provide a PR :)