1.16 Release Notes - Add Known CoreDNS metrics regression

[gjtempleton]

Replacement for #8587

As per discussion at office hours.

I've followed the style and syntax as much as possible from upstream k/k given we haven't had known issues blocks since 1.6, open to feedback especially as it doesn't actually apply to all releases in the 1.16 train.

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[rifelpet]

Any reason this shouldn't also be mentioned in 1.17 and 1.18 release notes? Are we hoping to have upgraded to 1.6.7 in those branches?

[rajansandeep]

The coredns version 1.6.7 is now made available in gcr.io (This would be the version in upstream k/k 1.18)

$ docker pull k8s.gcr.io/coredns:1.6.7
1.6.7: Pulling from coredns
Digest: sha256:2c8d61c46f484d881db43b34d13ca47a269336e576c81cf007ca740fa9ec0800
Status: Downloaded newer image for k8s.gcr.io/coredns:1.6.7

[gjtempleton]

I was assuming that the 1.6.7 publish to k8s.gcr.io would happen before 1.17 and 1.18 hit GA. Seems it happened even faster than anticipated.

I guess in that case time to close this PR and re-pick the updates into the release branches then.