Add option to configure default platforms

[ReToCode]

Adds an option to configure default platforms either in .ko.yaml or using the env variable KO_DEFAULTPLATFORMS.

Fixes #521

[ReToCode]

@imjasonh something like this? Unfortunately there is no easy way to test this properly without either

• exposing internals of gobuildOpener to test this from resolver_test.go
• or extending the build.Interface interface similar to QualifyImport to test it in resolver_test.go

WDYT?

[imjasonh]

This looks great! This is honestly even less code than I thought it would be. 👍

The test seems fine. Maybe worth adding another .ko.yaml that has defaultPlatforms: foo,bar just to make sure it handles splitting on , in the config as we expect.

[ReToCode]

I added another test case but not with splitting , as viper expects a yaml array to be parsed as a string slice. I also changed the docs accordingly.

[imjasonh]

Nice, that test covers exactly what I was hoping to find out!

[codecov-commenter]

Codecov Report

Merging #897 (b4371bc) into main (a28ed35) will increase coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #897      +/-   ##
==========================================
+ Coverage   51.33%   51.34%   +0.01%     
==========================================
  Files          44       44              
  Lines        3407     3414       +7     
==========================================
+ Hits         1749     1753       +4     
- Misses       1430     1432       +2     
- Partials      228      229       +1     

Impacted Files	Coverage Δ
pkg/commands/resolver.go	36.55% <0.00%> (-0.34%)	⬇️
pkg/commands/options/build.go	71.07% <100.00%> (+0.98%)	⬆️

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[ReToCode]

Seems like there was already an empty line in that file which is not really visible in GitHub.

[imjasonh]

Thanks again for this contribution, and for fighting through the lint checks for it! 😅