[v0.13.x] - Expose CoreDNS to Prometheus

[dominicgunn]

Changes

• Updates the CoreDNS service deployment to allow scraping by Prometheus.
• This matches the Kubernetes upstream CoreDNS addon deployment, shown here

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #1636 into v0.13.x will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           v0.13.x    #1636   +/-   ##
========================================
  Coverage    25.49%   25.49%           
========================================
  Files           98       98           
  Lines         5049     5049           
========================================
  Hits          1287     1287           
  Misses        3619     3619           
  Partials       143      143

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