[Tracking Upstream] Bump openshift/coredns to the latest upstream release

As a cluster administrator,

I want OpenShift to include a recent CoreDNS version,

so that I have the latest available performance and security fixes.

We should strive to follow upstream CoreDNS releases by bumping openshift/coredns with every OpenShift 4.y release, so that OpenShift benefits from upstream performance and security fixes, and so that we avoid large version-number jumps when an urgently needed change necessitates bumping CoreDNS to the latest upstream release. This bump should happen as early as possible in the OpenShift release cycle, so as to maximize soak time.

For OpenShift 4.9, this means bumping from CoreDNS 1.8.1 to 1.8.3, or possibly a later release should one ship before we do the bump.

Note that CoreDNS upstream does not maintain release branches—that is, once CoreDNS is released, there will be no further 1.8.z releases—so we may be better off updating to 1.9 as soon as it is released, rather than staying on the 1.8 series which would then be unmaintained.

We may consider bumping CoreDNS again during the OpenShift 4.9 release cycle if upstream ships additional releases during the 4.9 development cycle. However, we will need to weigh the risks and available remaining soak time in the release schedule before doing so, should that contingency arise.