Add a krane tool.

[mattmoor]

This adds a krane tool, which is effectively crane with a multi-keychain that prefers default authentication mechanisms, but links k8schain as a fallback.

This enables this tool to act as a drop-in replacement for crane, but it can support common Kubernetes-based workload identity mechanisms.

[codecov-commenter]

Codecov Report

Merging #1218 (639e5d4) into main (2874338) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1218   +/-   ##
=======================================
  Coverage   73.76%   73.76%           
=======================================
  Files         111      111           
  Lines        8181     8181           
=======================================
  Hits         6035     6035           
  Misses       1549     1549           
  Partials      597      597           

---

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[jonjohnsonjr]

Step #0: + ./ko publish --platform=all -B github.com/google/go-containerregistry/cmd/krane -t latest -t 3889fab028df2dc8c5402ee23612c3e99e9621dc -t 
Step #0: 2021/12/29 18:38:15 Using base gcr.io/distroless/static:nonroot for github.com/google/go-containerregistry/cmd/krane
Step #0: 2021/12/29 18:38:15 Building github.com/google/go-containerregistry/cmd/krane for linux/amd64
Step #0: 2021/12/29 18:38:16 Unexpected error running "go build": exit status 1
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:24:2: cannot find package "github.com/vdemeester/k8s-pkg-credentialprovider" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/github.com/vdemeester/k8s-pkg-credentialprovider (vendor tree)
Step #0: 	/usr/local/go/src/github.com/vdemeester/k8s-pkg-credentialprovider (from $GOROOT)
Step #0: 	/go/src/github.com/vdemeester/k8s-pkg-credentialprovider (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain_aws.go:22:2: cannot find package "github.com/vdemeester/k8s-pkg-credentialprovider/aws" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/github.com/vdemeester/k8s-pkg-credentialprovider/aws (vendor tree)
Step #0: 	/usr/local/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/aws (from $GOROOT)
Step #0: 	/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/aws (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain_azure.go:22:2: cannot find package "github.com/vdemeester/k8s-pkg-credentialprovider/azure" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/github.com/vdemeester/k8s-pkg-credentialprovider/azure (vendor tree)
Step #0: 	/usr/local/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/azure (from $GOROOT)
Step #0: 	/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/azure (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain_gcp.go:22:2: cannot find package "github.com/vdemeester/k8s-pkg-credentialprovider/gcp" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/github.com/vdemeester/k8s-pkg-credentialprovider/gcp (vendor tree)
Step #0: 	/usr/local/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/gcp (from $GOROOT)
Step #0: 	/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/gcp (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:25:2: cannot find package "github.com/vdemeester/k8s-pkg-credentialprovider/secrets" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/github.com/vdemeester/k8s-pkg-credentialprovider/secrets (vendor tree)
Step #0: 	/usr/local/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/secrets (from $GOROOT)
Step #0: 	/go/src/github.com/vdemeester/k8s-pkg-credentialprovider/secrets (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:26:2: cannot find package "k8s.io/api/core/v1" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/k8s.io/api/core/v1 (vendor tree)
Step #0: 	/usr/local/go/src/k8s.io/api/core/v1 (from $GOROOT)
Step #0: 	/go/src/k8s.io/api/core/v1 (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:27:2: cannot find package "k8s.io/apimachinery/pkg/apis/meta/v1" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/k8s.io/apimachinery/pkg/apis/meta/v1 (vendor tree)
Step #0: 	/usr/local/go/src/k8s.io/apimachinery/pkg/apis/meta/v1 (from $GOROOT)
Step #0: 	/go/src/k8s.io/apimachinery/pkg/apis/meta/v1 (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:28:2: cannot find package "k8s.io/client-go/kubernetes" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/k8s.io/client-go/kubernetes (vendor tree)
Step #0: 	/usr/local/go/src/k8s.io/client-go/kubernetes (from $GOROOT)
Step #0: 	/go/src/k8s.io/client-go/kubernetes (from $GOPATH)
Step #0: /go/src/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go:29:2: cannot find package "k8s.io/client-go/rest" in any of:
Step #0: 	/go/src/github.com/google/go-containerregistry/vendor/k8s.io/client-go/rest (vendor tree)
Step #0: 	/usr/local/go/src/k8s.io/client-go/rest (from $GOROOT)
Step #0: 	/go/src/k8s.io/client-go/rest (from $GOPATH)
Step #0: 2021/12/29 18:38:16 failed to publish images: error building "ko://github.com/google/go-containerregistry/cmd/krane": exit status 1

[mattmoor]

I believe the problem is that we do a ko publish of the ./cmd/krane sub-module while our current directory is the GGCR module still, which I think confuses things. Locally this works just fine if I'm in ./cmd/krane, and I'm testing a change to cloudbuild.yaml against my own project now.