Simple kubectl plugin for plan functionality

We would like to modularize kpt into composable functionality.  Start
with creating a kubectl plugin that can hold "plan" functionality.

plugins/cmd/kubectl-plan/README.md

@@ -0,0 +1,7 @@
+# kubectl-plan
+
+kubectl-plan is an experimental kubectl plugin that dry-runs
+apply operations and shows the changes in an easy to read format.
+
+It is still under development and highly experimental, it should
+not be treated as stable.

plugins/cmd/kubectl-plan/main.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/GoogleContainerTools/kpt/plugins/pkg/cmd/plan"
+)
+
+func main() {
+	if err := Run(context.Background()); err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
+}
+
+func Run(ctx context.Context) error {
+	root := plan.NewCommand()
+	return root.ExecuteContext(ctx)
+}

plugins/go.mod

@@ -0,0 +1,90 @@
+module github.com/GoogleContainerTools/kpt/plugins
+
+go 1.21.3
+
+require (
+	github.com/google/go-cmp v0.5.9
+	github.com/spf13/cobra v1.8.0
+	k8s.io/apimachinery v0.28.4
+	k8s.io/client-go v0.28.4
+	k8s.io/klog v1.0.0
+	k8s.io/klog/v2 v2.100.1
+	k8s.io/kubectl v0.28.4
+	oras.land/oras-go v1.2.4
+	sigs.k8s.io/kubebuilder-declarative-pattern v0.13.0
+	sigs.k8s.io/kubebuilder-declarative-pattern/mockkubeapiserver v0.0.0-20231030230424-f6a5c89244f2
+	sigs.k8s.io/kustomize/kyaml v0.15.0
+)
+
+require (
+	github.com/Azure/go-ansiterm v0.0.0-20210617225240-d185dfc1b5a1 // indirect
+	github.com/MakeNowJust/heredoc v1.0.0 // indirect
+	github.com/Microsoft/hcsshim v0.11.0 // indirect
+	github.com/chai2010/gettext-go v1.0.2 // indirect
+	github.com/containerd/containerd v1.7.6 // indirect
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/emicklei/go-restful/v3 v3.10.1 // indirect
+	github.com/evanphx/json-patch v4.12.0+incompatible // indirect
+	github.com/exponent-io/jsonpath v0.0.0-20151013193312-d6023ce2651d // indirect
+	github.com/go-errors/errors v1.4.2 // indirect
+	github.com/go-logr/logr v1.2.4 // indirect
+	github.com/go-openapi/jsonpointer v0.19.6 // indirect
+	github.com/go-openapi/jsonreference v0.20.2 // indirect
+	github.com/go-openapi/swag v0.22.3 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/golang/protobuf v1.5.3 // indirect
+	github.com/google/btree v1.0.1 // indirect
+	github.com/google/gnostic-models v0.6.8 // indirect
+	github.com/google/gofuzz v1.2.0 // indirect
+	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7 // indirect
+	github.com/imdario/mergo v0.3.13 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/josharian/intern v1.0.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/compress v1.16.0 // indirect
+	github.com/liggitt/tabwriter v0.0.0-20181228230101-89fcab3d43de // indirect
+	github.com/mailru/easyjson v0.7.7 // indirect
+	github.com/mitchellh/go-wordwrap v1.0.1 // indirect
+	github.com/moby/spdystream v0.2.0 // indirect
+	github.com/moby/term v0.0.0-20221205130635-1aeaba878587 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/monochromegane/go-gitignore v0.0.0-20200626010858-205db1a8cc00 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/opencontainers/go-digest v1.0.0 // indirect
+	github.com/opencontainers/image-spec v1.1.0-rc5 // indirect
+	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	github.com/sirupsen/logrus v1.9.3 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/xlab/treeprint v1.2.0 // indirect
+	go.starlark.net v0.0.0-20230525235612-a134d8f9ddca // indirect
+	golang.org/x/net v0.17.0 // indirect
+	golang.org/x/oauth2 v0.8.0 // indirect
+	golang.org/x/sync v0.3.0 // indirect
+	golang.org/x/sys v0.13.0 // indirect
+	golang.org/x/term v0.13.0 // indirect
+	golang.org/x/text v0.13.0 // indirect
+	golang.org/x/time v0.3.0 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20230525234030-28d5490b6b19 // indirect
+	google.golang.org/grpc v1.56.3 // indirect
+	google.golang.org/protobuf v1.31.0 // indirect
+	gopkg.in/evanphx/json-patch.v5 v5.6.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+	k8s.io/api v0.28.4 // indirect
+	k8s.io/cli-runtime v0.28.4 // indirect
+	k8s.io/component-base v0.28.4 // indirect
+	k8s.io/kube-openapi v0.0.0-20230717233707-2695361300d9 // indirect
+	k8s.io/utils v0.0.0-20230505201702-9f6742963106 // indirect
+	sigs.k8s.io/controller-runtime v0.13.0 // indirect
+	sigs.k8s.io/json v0.0.0-20221116044647-bc3834ca7abd // indirect
+	sigs.k8s.io/kustomize/api v0.15.0 // indirect
+	sigs.k8s.io/structured-merge-diff/v4 v4.2.3 // indirect
+	sigs.k8s.io/yaml v1.3.0 // indirect
+)