title: SortOrder by dropPrice Prestashop 1.7
body: <p>there are default sort orders in PS 1.7 like &gt;</p>
  <pre><code>(new SortOrder('product', 'price', 'asc'))........ 
  (new SortOrder('product', 'date_add', 'asc'))-&gt;setLabel(    etc etc
  </code></pre>
  <p>but what I want to know is that is it possible to get SortOrder by Price drop? so that it will show product by <code>asc</code> or des DropPrice list, which should be like</p>
  <pre><code>(new SortOrder('product', 'dropPrice', 'asc'))
  </code></pre>
  <p>I want to filter it by &quot;highest discounts &amp; Lowest discount&quot;. so the page will show products with the highest amount of discount &quot;<code>asc or dsc</code>&quot; &amp; vise versa.</p>
  <p>Hope you all get my point.</p>