[14.0][IMP] pos_payment_change: Datetime management

[jguenat]

I found that order/payment date had some strange behavior when modifying a payment, see #1325

Also fix a bug where the resale order was not at the same time as the refund order in case of refund policy.

In case of update policy keep payment_date the same In case of refund policy use current datetime for refund/resale order and payments

[OCA-git-bot]

Hi @legalsylvain, some modules you are maintaining are being modified, check this out!