title: Show sort arrow on Ext.grid on page load
body: <p>I have a grid that shows the product id as shown below. </p>
  
  <p><img src="https://i.stack.imgur.com/nZLSC.jpg" alt="enter image description here"></p>
  
  <p>​​The data is sorted with the product ID but the grid doesn't show the arrow initially. 
  If I click on the column then the arrow shows up. How do I make the sort arrows to show immediately on page load as shown below.</p>
  
  <p><img src="https://i.stack.imgur.com/t35hf.jpg" alt="enter image description here"></p>