[release-1.26] Allow adding configuration to coredns .:53 block via *.override keys in coredns-custom ConfigMap

[brandond]

• Allow adding configuration to coredns .:53 block via *.override keys in coredns-custom ConfigMap #7639 backport

[VestigeJ]

Attention to the line import /etc/coredns/custom/*.override

Existing release v1.26.5+k3s1
$ kg cm -n kube-system coredns -o yaml

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }
        hosts /etc/coredns/NodeHosts {
          ttl 60
          reload 15s
          fallthrough
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
    import /etc/coredns/custom/*.server
  NodeHosts: |
    1.1.2.143 ip-1-1-2-143
kind: ConfigMap
metadata:
  annotations:
    objectset.rio.cattle.io/applied: H4sIAAAAAAAA/4yQwWrzMBCEX0Xs2fEf20nsX9BDybH02lMva2kdq1Z2g6SkBJN3L8IUCiVtbyNGOzvfzoAn90IhOmHQcKmgAIsJQc+wl0CD8wQaSr1t1PzKSilFIUiIix4JfRoXHQjtdZHTuafAlCgq488xUSi9wK2AybEFDXvhwR2e8QQFHCnh50ZkloTJCcf8lP6NTIqUyuCkNJiSp9LJP5czoLjryztTWB0uE2iYmvjFuVSFenJsHx6tFf41gvGY6Y0Eshz/9D2e0OSZfIJVvMZExwzusSf/I9SIcQQNvaG6a+r/XVdV7abBddPtsN9W66Eedi0N7aberM22zaHf6t0tcPsIAAD//8Ix+PfoAQAA
    objectset.rio.cattle.io/id: ""
    objectset.rio.cattle.io/owner-gvk: k3s.cattle.io/v1, Kind=Addon
    objectset.rio.cattle.io/owner-name: coredns
    objectset.rio.cattle.io/owner-namespace: kube-system
  creationTimestamp: "2023-06-14T23:13:15Z"
  labels:
    objectset.rio.cattle.io/hash: bce283298811743a0386ab510f2f67ef74240c57
  name: coredns
  namespace: kube-system
  resourceVersion: "351"
  uid: 0763b6ef-077b-4187-964f-eee5e3f259ab

New INSTALL_K3S_COMMIT=f3b08c3863b7f3a7d6655e99077482353a54b309

$ kg cm -n kube-system coredns -o yaml

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }
        hosts /etc/coredns/NodeHosts {
          ttl 60
          reload 15s
          fallthrough
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
        import /etc/coredns/custom/*.override
    }
    import /etc/coredns/custom/*.server
  NodeHosts: |
    1.1.2.2 ip-1-1-2-2
kind: ConfigMap
metadata:
  annotations:
    objectset.rio.cattle.io/applied: H4sIAAAAAAAA/4yQwWrzMBCEX0Xs2fEf20nsX9BDybH02lMva2kdq1Z2g6SkBJN3L8IUCiVtbyNGOzvfzoAn90IhOmHQcKmgAIsJQc+wl0CD8wQaSr1t1PzKSilFIUiIix4JfRoXHQjtdZHTuafAlCgq488xUSi9wK2AybEFDXvhwR2e8QQFHCnh50ZkloTJCcf8lP6NTIqUyuCkNJiSp9LJP5czoLjryztTWB0uE2iYmvjFuVSFenJsHx6tFf41gvGY6Y0Eshz/9D2e0OSZfIJVvMZExwzusSf/I9SIcQQNvaG6a+r/XVdV7abBddPtsN9W66Eedi0N7aberM22zaHf6t0tcPsIAAD//8Ix+PfoAQAA
    objectset.rio.cattle.io/id: ""
    objectset.rio.cattle.io/owner-gvk: k3s.cattle.io/v1, Kind=Addon
    objectset.rio.cattle.io/owner-name: coredns
    objectset.rio.cattle.io/owner-namespace: kube-system
  creationTimestamp: "2023-06-14T23:13:18Z"
  labels:
    objectset.rio.cattle.io/hash: bce283298811743a0386ab510f2f67ef74240c57
  name: coredns
  namespace: kube-system
  resourceVersion: "371"
  uid: d089ee66-e015-4d4d-946c-337c3bfb95f8

$ cat coredns-customize.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns-custom
  namespace: kube-system
data:
  log.override: |
    log
  custom.server: |
    why.local {
      forward . 127.0.0.1
    }