Adding a additional sort option in product collection page

Summary

How to add additional sort option based on a sku property in Product Listing Js

Content

Hi,

We have a sort by dropdown with standard sort option Price Low to high and Price High to Low, we need to add additional sort options "Capacity High to Low" which should take value from a sku variant property.

How do we access the sku property to provide in the "id"  field below :

 var sortOptions = [{
          "id": "???",
          "displayText": "Capacity Low to High",
          "order": ko.observable("asc"),
          "maintainSortOrder": true,
          "serverOnly": true
        }]