Provide access to the allowUnknownOption complaints

[JoshuaKGoldberg]

There's no way I can find to find which args are unsupported. In this

program..allowUnknownOption();

// error on unknown commands
program.on('command:*', function () {
  console.error('Invalid command: %s\nSee --help for a list of available commands.', program.args.join(' '));
  process.exit(1);
});

The function receives no arguments and command.args is empty in my usage. Can there be a command.unknownOptions added to store the ones added?

[shadowspawn]

Closing in favour of #802

Thank you for your contributions.