Make PO number mandatory (at quote approval), so it carries into the PSA for procurement

Please add a feature to make PO numbers mandatory for customers, so the customer always receives a dedicated invoice for the quote.

Additional context (Xantion ICT, Autotask): make the PO number field mandatory at the moment the quote is approved. The benefit is that the PO number is then carried through to Autotask and automatically filled in for the purchasing process, which removes a lot of manual work.