AMP Camp: related products don't work when you click on item from cart

[morsssss]

This happens because the cart items don't contain a category ID, which is what our related products relies on. So, you're at a URL like https://camp.samples.amp.dev/product-details?productId=M0871 instead of https://camp.samples.amp.dev/product-details?categoryId=men-shorts&productId=M0871.