Resolve in-addr.arpa and ip6.arpa zones with CoreDNS kubernetes plugin

[dghubble]

• Resolve in-addr.arpa and ip6.arpa DNS PTR requests for Kubernetes service IPs and pod IPs
• Previously, CoreDNS was configured to resolve in-addr.arpa PTR records for service IPs (but not pod IPs)

Before:

$ dig 1.0.3.10.in-addr.arpa PTR
...
1.0.3.10.in-addr.arpa.  5       IN      PTR     kubernetes.default.svc.cluster.local.
$ 8.1.2.10.in-addr.arpa PTR
8.1.2.10.in-addr.arpa.  30      IN      PTR     ip-10-2-1-8.CLOUD_SPECIFIC_UPSTREAM

After:

$ dig 1.0.3.10.in-addr.arpa PTR
...
1.0.3.10.in-addr.arpa.  5       IN      PTR     kubernetes.default.svc.cluster.local.
$ 8.1.2.10.in-addr.arpa PTR
8.1.2.10.in-addr.arpa.  30      IN      PTR     10-2-1-8.prometheus.monitoring.svc.cluster.local.

Related:

• https://coredns.io/plugins/kubernetes/
• Resolve in-addr.arpa and ip6.arpa zones with CoreDNS kubernetes plugin terraform-render-bootstrap#118