[coredns] missing forward metrics in recent release

[Art3mK]

Hey, looks like coredns needs some updates for metrics collected, at least for forward plugin.

In readme file they state some metrics were deprecated (in 2023? 😁):

The following metrics have recently been deprecated:
coredns_forward_healthcheck_failures_total{to, rcode}
Can be replaced with coredns_proxy_healthcheck_failures_total{proxy_name="forward", to, rcode}
coredns_forward_requests_total{to}
Can be replaced with sum(coredns_proxy_request_duration_seconds_count{proxy_name="forward", to})
coredns_forward_responses_total{to, rcode}
Can be replaced with coredns_proxy_request_duration_seconds_count{proxy_name="forward", to, rcode}
coredns_forward_request_duration_seconds{to, rcode}
Can be replaced with coredns_proxy_request_duration_seconds{proxy_name="forward", to, rcode}

So for example new node-local-dns image doesn't have metrics coredns integration is looking for:

old image (registry.k8s.io/dns/k8s-dns-node-cache:1.22.28):
➜  curl http://10.1.157.105:9253/metrics | grep forward_request_duration
# TYPE coredns_forward_request_duration_seconds histogram
coredns_forward_request_duration_seconds_bucket{rcode="NOERROR",to="10.1.0.2:53",le="0.00025"} 248
coredns_forward_request_duration_seconds_bucket{rcode="NOERROR",to="10.1.0.2:53",le="0.0005"} 476
coredns_forward_request_duration_seconds_bucket{rcode="NOERROR",to="10.1.0.2:53",le="0.001"} 961
...
# newest image (registry.k8s.io/dns/k8s-dns-node-cache:1.26.5)
➜  curl http://10.0.38.174:9253/metrics | grep forward_request_duration
<%nothing%>
# but there is for example:
coredns_proxy_request_duration_seconds_bucket{proxy_name="forward",rcode="NXDOMAIN",to="172.20.143.13:53",le="0.0005"} 562

Thanks!