title: Specify order of ARIMA using Fable package
body: <p>I am running an ARIMA model using the <code>fable</code> package. Just curious to find out whether there is a way to specify the order of the model (e.g specifying an order of 2,1,1) when using the <code>ARIMA</code> function in the package as opposed to using the optimal lags which are specified automatically?</p>
  <p>Also trying to figure out the best way to add a vector as a dummy variable in order to control for a structural break for the first observation</p>
  <p>I've used the built in dataset in the package (<code>tourism</code>)</p>
  <pre><code>library(fable)
  
  fit &lt;- tourism %&gt;% slice(tail(row_number(), 10)) %&gt;% 
    model(arima = ARIMA(Trips))
  
  </code></pre>
  <p>TIA!</p>