Ringfence stock for pre-order

As Create "On Hold" or "Quarantined" product stage is now done and 🏭 All orders & deliveries are now linked to a fulfillment site, allowing for available stock per site to be calculated was launched yesterday, I think these should cover off their feature request fairly well.

If anything extra is needed relating to pre-order stock reservation, can you please comment on Improved management of pre-orders and reservations with more information (and vote for it)? It would be helpful for us to keep all pre-order based suggestions on that one thread.

Thank you, everyone :+1: