feat: add support for Kubernetes 1.19.0-alpha.1

[mboersma]

Reason for Change:
See https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.19.md#v1190-alpha1

Issue Fixed:

Requirements:

• Kubernetes artifacts built and pushed by Azure Pipelines
• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
I added 1.19 to the PR mix, but we can drop that commit if need be to keep our cloud footprint minimal.

[codecov]

Codecov Report

Merging #2982 into master will decrease coverage by 0.51%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2982      +/-   ##
==========================================
- Coverage   72.58%   72.06%   -0.52%     
==========================================
  Files         141      141              
  Lines       25893    26186     +293     
==========================================
+ Hits        18794    18871      +77     
- Misses       6005     6221     +216     
  Partials     1094     1094              

Impacted Files	Coverage Δ
pkg/api/common/versions.go	96.55% <ø> (ø)
pkg/engine/templates_generated.go	31.69% <ø> (-3.13%)	⬇️
pkg/api/k8s_versions.go	100.00% <100.00%> (ø)

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[jackfrancis]

1.19 surface area looks good. Let's omit the additional 1.19 pipeline job before merging, after getting functional signal on this PR.

[mboersma]

Had a passing run with 1.19 on the second try, and it has passed e2e for me locally. So I'll discard the 1.19 e2e testing commit now.

[jackfrancis]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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