Add presubmit workflow

[jonjohnsonjr]

Fix all the things that it caught :(

[codecov-commenter]

Codecov Report

Merging #994 (1db72c4) into main (37467b5) will increase coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #994      +/-   ##
==========================================
+ Coverage   75.18%   75.19%   +0.01%     
==========================================
  Files         107      107              
  Lines        5061     5064       +3     
==========================================
+ Hits         3805     3808       +3     
  Misses        711      711              
  Partials      545      545              

Impacted Files	Coverage Δ
pkg/v1/layout/write.go	49.16% <0.00%> (ø)
pkg/registry/manifest.go	93.33% <100.00%> (+0.03%)	⬆️
pkg/registry/registry.go	100.00% <100.00%> (ø)

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[imjasonh]

We don't actually need master and release-* right?

[jonjohnsonjr]

If we need to patch release branches, we'll want that (I think).

All our other workflows work against master, and this has been useful for me. I keep my fork's default branch as master to easily (and lazily) differentiate it from this repo's main branch, so I don't accidentally push the wrong thing ever.