Add 'ko build' as a preferred alias for 'ko publish'

[imjasonh]

Fixes #451

[codecov-commenter]

Codecov Report

Merging #456 (7249a9e) into main (688ca47) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #456      +/-   ##
==========================================
+ Coverage   53.25%   53.28%   +0.02%     
==========================================
  Files          36       36              
  Lines        1842     1843       +1     
==========================================
+ Hits          981      982       +1     
  Misses        710      710              
  Partials      151      151              

Impacted Files	Coverage Δ
pkg/build/gobuild.go	58.44% <100.00%> (ø)
pkg/commands/build.go	68.75% <100.00%> (ø)
pkg/commands/commands.go	75.00% <100.00%> (ø)
pkg/commands/run.go	26.76% <100.00%> (ø)

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