Put k8schain in its own go module

[jonjohnsonjr]

This should make go-containerregistry much easier to use.

#902
ko-build/ko#287
ko-build/ko#258 (comment)

WANT_LGTM=all

[codecov-io]

Codecov Report

Merging #904 (d7daec0) into master (f97c411) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #904      +/-   ##
==========================================
- Coverage   72.60%   72.57%   -0.04%     
==========================================
  Files         108      108              
  Lines        4687     4689       +2     
==========================================
  Hits         3403     3403              
- Misses        774      776       +2     
  Partials      510      510              

Impacted Files	Coverage Δ
pkg/crane/digest.go	27.77% <0.00%> (-3.48%)	⬇️

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[jonjohnsonjr]

Per https://pkg.go.dev/github.com/google/go-containerregistry/pkg/authn/k8schain?tab=importedby y'all might be affected.

cc @andreyvelich
cc @scothis
cc @matthewmcnew
cc @hasheddan
cc @davidewatson (also, https://github.com/davidewatson/keychain looks interesting, would love to see a README 😉)
cc @leogr

[jonjohnsonjr]

Split this up into two commits:

1. go.mod changes, should be easy to review
2. go mod tidy && go mod vendor

I didn't vendor the k8schain deps because I think it might break some expectations of various tools (only one top-level vendor/ directory). That's why there's the huge negative diff. Hopefully that's fine.

[mattmoor]

Did you add any presubmit safeguard that the nested module files are correct?

[jonjohnsonjr]

cc @tejal29 as well

[jonjohnsonjr]

Did you add any presubmit safeguard that the nested module files are correct?

Done: 52dc010

[hasheddan]

Thanks @jonjohnsonjr! I'll test this out with our @crossplane usage 👍

[andreyvelich]

Thank you for the notice @jonjohnsonjr!
cc @gaocegege @johnugeorge

[mattmoor]

the parent is 1.14, these should be consistent.

[jonjohnsonjr]

I think it would be fine for them to diverge in the future, but I've dropped this to 1.14.