Backend: Endpoint to create invoice

[enzofalone]

• Create invoice must take values of: date, sold to
  • Create reference rows in relation to items that will be invoiced with: base price, sales price and to what invoice ID they are
  • Calculate total price of invoice column by adding up all the item's price
  • Decrease the quantity as how many were sold
  • Throw error if quantity that is trying to be invoiced of any item is greater than the quantity of the items is