Feat: disable items selector section if invoice is return invoice.

[Madcheese101]

https://github.com/yrestom/POS-Awesome/assets/40042269/e1b110b3-ec25-47a7-a945-8d5d595c0a4d

[CloudERPng]

This is nice, can this be an option in PoS Profile?

@yrestom this is not a bad feature, quite useful for control purposes

[Madcheese101]

@CloudERPng It can, but it is best to leave it as default because it would contradict the logic of returning an invoice.

when returning an invoice the employee should not be allowed to add new items and only allows the employee to edit the original content of the sale invoice. This allows for fewer validations on the server/client side and fewer mistakes from the employee.