feat: add support for Kubernetes 1.19.0-alpha.3

[mboersma]

Reason for Change:
See https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.19.md#changelog-since-v1190-alpha2

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 were several APIs deprecated with this release, but I think we should defer updating them. See #3196.

[codecov]

Codecov Report

Merging #3197 into master will decrease coverage by 2.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3197      +/-   ##
==========================================
- Coverage   71.15%   68.97%   -2.19%     
==========================================
  Files         147      147              
  Lines       25768    27725    +1957     
==========================================
+ Hits        18336    19124     +788     
- Misses       6286     7366    +1080     
- Partials     1146     1235      +89     

Impacted Files	Coverage Δ
pkg/api/common/versions.go	96.55% <ø> (ø)
pkg/api/addons.go	97.88% <0.00%> (+<0.01%)	⬆️
pkg/api/components.go	96.95% <0.00%> (+0.06%)	⬆️
pkg/engine/templates_generated.go	39.14% <0.00%> (+0.77%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 163129c...178f2d4. Read the comment docs.

[mboersma]

/hold

There's a temporary testing commit here that should be discarded.

[mboersma]

The 1.19 PR run passed, so I stripped off the test commit and this should be ready for review.

[mboersma]

/hold cancel

[mboersma]

I honestly don't know where CodeCov is coming from these days. This is a one-line change to one .go file. We need to rationalize our coverage numbers somehow, because I haven't found its report to be useful for months now.

Edit: see #3203.

[jackfrancis]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [jackfrancis,mboersma]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment