Autogenerate JSON Schema and Documentation

Typescript Blueprints shipped a JSON Schema and documentation generated from the TypeScript source:

https://github.com/WordPress/wordpress-playground/blob/ef1eb3f57ee251ec98f6075ff7e83d22add188e0/packages/playground/blueprints/public/blueprint-schema.json

The PHP version could do the same to ensure the schema and the documentation are always up to date with the code. This may require taking specific design choices, such as shipping steps arguments as classes:

class WriteFileStepArgs implements StepArgs {
	public $file;
	public string $toPath;

	/**
	 * @param $file
	 * @param string $toPath
	 */
	public function __construct( $file, string $toPath ) {
		$this->file   = $file;
		$this->toPath = $toPath;
	}

}

Start by comparing the TypeScript generator in packages/playground/blueprints/bin/generate-schema.js with the checked-in public/blueprint-schema.json linked in the issue, then inspect the PHP blueprint source and its step argument definitions. Define how PHP arguments should be represented before implementing generation; done means the PHP schema and documentation are generated from the code and remain up to date.