refactor: consolidate kube-dns addon spec

[jackfrancis]

Reason for Change:

Eases maintenance of the kube-dns addon by consolidating manifests into a single YAML file that uses Go templating.

Issue Fixed:

Addresses #3188.

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3390 into master will increase coverage by 0.02%.
The diff coverage is 36.84%.

@@            Coverage Diff             @@
##           master    #3390      +/-   ##
==========================================
+ Coverage   72.67%   72.70%   +0.02%     
==========================================
  Files         147      147              
  Lines       25170    25170              
==========================================
+ Hits        18293    18300       +7     
+ Misses       5745     5737       -8     
- Partials     1132     1133       +1     

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	49.16% <36.84%> (+0.43%)	⬆️

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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[acs-bot]

New changes are detected. LGTM label has been removed.