[FIX] payment: use currency precision when comparing amounts in Payment Link wizard

In Sales, in Payment Link generation wizard, when entering manually the total of the quotation
as Amount, it can happen that the Validation Error asking to set an Amount smaller than the total
is triggered.

opw-2287794

closes odoo/odoo#54278

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>