Release Go-native tool

[cardil]

Rewrite release.sh script (https://github.com/knative/hack/blob/main/README.md#using-the-releasesh-helper-script) into a Golang tool knative.dev/toolbox/releaser.

Invent new Go-native extension interface, for example:

# will look for Go files with `release` build constraints, that register build configuration
go run knative.dev/toolbox/releaser@latest ./ \
  --dot-release \
  --release-gcs knative-releases/kn-plugin-event \
  --release-gcr gcr.io/knative-releases \
  --github-token /etc/hub-token/token \
  --apple-codesign-key /etc/notary/cert.p12 \
  --apple-notary-api-key /etc/notary/key.json \
  --apple-codesign-password-file /etc/notary/password \
  --branch release-1.9

The release configuration might look like:

//go:build release
package serving

import (
  "fmt"
  "os"

  // Implemented with `github.com/bitfield/script` or similar
  "knative.dev/pkg/kscript/ko"
  "knative.dev/toolbox/releaser/pkg/config"
)

init {
  config.Configure(function(ctx config.Context) {
    f := must[*os.File](ko.Resolve("config").AsFile("release.yaml"))
    ctx.AddAsArtifact(f)
  })
}

func must[T any](ret T, err error) T {
  if err != nil {
    panic(err)
  }
  return ret
}

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[cardil]

/reopen
/remove-lifecycle stale
/triage accepted

[knative-prow]

@cardil: Reopened this issue.

In response to this:

/reopen
/remove-lifecycle stale
/triage accepted

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