feat: add support for stdin JSON input

[aduh95]

The goal is to remove the need to clone the repo in https://github.com/nodejs/node/blob/main/.github/workflows/notify-on-push.yml, and instead rely on push.commits like so:

- name: Validate commits
  run: echo "$COMMITS" | npx -q core-validate-commit -
  env:
    COMMITS: ${{ toJSON(github.event.commits) }}

[JakobJingleheimer]

Thanks for handling this :)

[JakobJingleheimer]

This seems a little convoluted. Could it be done with a simple loop?

Suggested change

	args.splice(0, 1, ...commits.map(commit => {
	if (!commit.id || !commit.message) {
	throw new Error('Each commit must have "id" and "message" properties')
	}
	return { sha: commit.id, ...commit }
	}))
	for (let i = 0; i < commits.length; i++) {
	if (!commit.id || !commit.message) {
	throw new Error('Each commit must have "id" and "message" properties')
	}
	args[i] = { sha: commit.id, ...commit }
	}

[JakobJingleheimer]

nit: I think the else is not necessary (just return) and only creates messier nesting.

also nit: since the "is tap" block is larger, I would invert it to avoid nesting:

if (!parsed.tap) {
  v.on('commit', (c) => {
    pretty(c.commit, c.messages, v)
    commitRun()
  })

  return commitRun()
}

const tap = new Tap()
// …

[JakobJingleheimer]

nit: not sure if the current is required by the cumbersome lint rules of this repo, but the ) not being on its own line makes this very difficult to read.

[JakobJingleheimer]

This seems likely to create bad DX. If it's not an array, just wrap it in an array.