SDK doesn't accurately represent task types

[matt-sanders]

We've recently tried using the SDK to create tasks with some more advanced properties such as timeoutSeconds and pollTimeoutSeconds. These are not present in the SDK ( and aren't very obvious in the docs either ). It's required us to do something like:

const task = {
  ...simpleTask('someRef', 'someTask', {}),
  taskDefinition: {
    timeoutSeconds: 300,
    pollTimeoutSeconds: 300
  }
}

It'd be great if the SDK supported these options.