feat: Unit Price Items

[marination]

no-docs
Closes #36012 (Refer for more Info)
Revival of #36024 in a hopefully cleaner way

WIP: 🚧 🚧 🚧 🚧 🚧 🚧 🚧 🚧 🚧 🚧

• 
• We now flag the record as has_unit_price_items if allowed via Settings and if it has any 0 qty items
• We don't maintain row wise flags anymore. The user is free to leave the qty as 0. Nothing more
• They will be reminded that the record contains unit price items
  

Users can decide to manage their Transactions in two ways

1. Keep updating the Qty in the Order ["Sales Order", "Purchase Order"]
   • Once a portion of work is done, users can update the qty in the SO/PO -> Then create SI/PI for the updated qty
2. Keep the Qty 0 [SO, PO, RFQ, SQ, Quotation]
   • For those who might think constant updation SO is adding friction OR are not particular about tracking OR cannot update quantities in certain documents after submission, you can leave the quantities to be 0.
   • They can keep making Invoices with actual quantities against the SO/PO with 0 qty. The Billed % will always show as 0
   • The SO/PO will have to be manually Closed. Since there's no way to know when the Order is truly Completed.

TODO:

• Extend to Purchase
• Tests
• Docs