Add a cancel order function

At the moment, orders time out and invoices expire but there is no explicit way to cancel an order. Users should be able to hit a cancel order button at any stage and have their escrow/hold invoice released.

This is possible using the documentation here https://github.com/daywalker90/holdinvoice?tab=readme-ov-file#installation

I would add this is as a backend function, test it and then add the button in a seperate issue in the frontend repo.