Allow Per-Product Shipping to be added on top of other Shipping Options
Currently, if the `Enable per-product shipping method for vendors` option is selected:
It will show that shipping cost only as a separate shipping option at checkout (next to any other ones that are setup).
In this screenshot, you can see that the per-product shipping cost is $5.50, and then there are other shipping options available:
It would be great if there was also an option to add the $5.50 cost on top of the other methods, instead of as it's own method (this is available in Per Product Shipping(https://www.woocommerce.com/products/per-product-shipping/) itself, but not the included functionality within this extension). So, using the example screenshot above the "FedEx Standard Overnight" cost would go to $41.76 and the "FedEx 2Day" cost would go to $30.88 (or have that influence any flat rates, etc. that are setup).