Introduce v1alpha4 config version

[dgageot]

Signed-off-by: David Gageot david@gageot.net

[codecov-io]

Codecov Report

Merging #1062 into master will increase coverage by 0.05%.
The diff coverage is 55.31%.

@@            Coverage Diff             @@
##           master    #1062      +/-   ##
==========================================
+ Coverage    40.8%   40.86%   +0.05%     
==========================================
  Files          70       70              
  Lines        3088     3091       +3     
==========================================
+ Hits         1260     1263       +3     
  Misses       1703     1703              
  Partials      125      125

Impacted Files	Coverage Δ
pkg/skaffold/deploy/kubectl/cli.go	0% <ø> (ø)	⬆️
pkg/skaffold/build/gcb/cloud_build.go	0% <0%> (ø)	⬆️
pkg/skaffold/build/local/bazel.go	0% <0%> (ø)	⬆️
pkg/skaffold/deploy/kustomize.go	36.23% <0%> (ø)	⬆️
pkg/skaffold/config/config.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/init.go	0% <0%> (ø)	⬆️
pkg/skaffold/build/local/types.go	0% <0%> (ø)	⬆️
pkg/skaffold/build/gcb/types.go	0% <0%> (ø)	⬆️
pkg/skaffold/runner/timings.go	15.15% <0%> (ø)	⬆️
pkg/skaffold/build/local/local.go	62.5% <100%> (ø)	⬆️
... and 12 more

---

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[balopat]

@dgageot this looks great, thanks for introducing the latest aliases +100
kokoro failed with the upgrade test, otherwise LGTM:

  --- FAIL: TestFix/test_v1alpha3_to_v1alpha4_fix (0.09s)
    	run_test.go:265: testing error: exit status 1

[balopat]

lgtm after the kokoro fix