For customer invoices:
* do not set default date because if you prepare an invoice (and it gets
  a default date), then validate it the next day, the date will be wrong
* set the date when posting if it wasn't set, because why not?

For vendor bills:
* do not set default date because you rarely encode a bill at the bill
  date. Forcing the user to enter it reduces risks of user error
  (duplicated vendor bill)
* do not set it when posting, same reason.

opw-2492862
Related #68368
Closes #68367

closes odoo/odoo#68689

Related: odoo/enterprise#17502
Signed-off-by: Laurent Smet <smetl@users.noreply.github.com>

- Install product_margin
- Go to Invoicing > Customers > Invoices and create an Invoice
- Add a Credit Note
- Go to Accounting > Reporting > Product Margins and check Product used in the Invoice
The "Avg. Sale Unit Price" is incorrect. It should be 0 as it is for "# Invoiced in Sale"

Credit Notes are not taken into consideration when computing "Avg. Sale Unit Price".
This is also the case for discount.

opw-2382797

closes odoo/odoo#65583

X-original-commit: a3ee7adff2b0662ae8875e1eab13228c165f5428
Signed-off-by: Anh Thao PHAM <kitan191@users.noreply.github.com>