feat: add support for Kubernetes 1.19.0-alpha.2

[mboersma]

Reason for Change:
See https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.19.md#changelog-since-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:
There is a problem building 1.19.0-alpha.2 currently in the Azure Pipeline. I will update this PR when we have it fixed. cc: @sozercan

[mboersma]

This PR contains a temporary commit to run CI for 1.19. This commit should be discarded before merging.

[codecov]

Codecov Report

Merging #3122 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3122      +/-   ##
==========================================
- Coverage   71.05%   71.04%   -0.02%     
==========================================
  Files         147      147              
  Lines       25671    25679       +8     
==========================================
+ Hits        18241    18244       +3     
- Misses       6294     6297       +3     
- Partials     1136     1138       +2     

Impacted Files	Coverage Δ
pkg/api/common/versions.go	96.55% <ø> (ø)
pkg/engine/templates_generated.go	37.76% <ø> (ø)
pkg/api/converterfromapi.go	93.60% <0.00%> (-0.34%)	⬇️
pkg/api/convertertoapi.go	93.12% <0.00%> (-0.31%)	⬇️
pkg/api/types.go	94.37% <0.00%> (-0.09%)	⬇️
pkg/api/defaults.go	92.47% <0.00%> (+0.02%)	⬆️

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[mboersma]

This passed CI (modulo the "artifact upload" error), so I'll discard the testing commit and it should be ready for review.

[jackfrancis]

/lgtm