CoreDNS support for PFSsense

[tvdv]

This PR adds basic CoreDNS support to pfSense

CoreDNS is useful on pfSense for custom/complex DNS configurations (e.g. split-DNS).

Here is an example CoreDNS configuration that will use a different forwarder, based on client IP. This example implements cloud-flare's family DNS blocking for some clients(192.168.2.0/24) and not others (192.168.1.0/24).

. {
  view familyfriendly {
    expr incidr(client_ip(), '192.168.2.0/24')
  }
  hosts /etc/hosts {
    1.1.1.3 testname 
    fallthrough
 }
 forward . tls://1.1.1.3 tls://1.0.0.3 {
    tls_servername family.cloudflare-dns.com
    policy random
    health_check 50s
 }
}

. {
  view default {
    expr incidr(client_ip(), '192.168.1.0/24')
  }
  hosts /etc/hosts {
    1.1.1.1 testname 
    fallthrough
 }
 forward . tls://1.1.1.1 tls://1.0.0.1 {
    tls_servername cloudflare-dns.com
    policy random
    health_check 50s
 }
}