Makes the `product.packaging` `product_id` required in the model instead
of the view only, since a packaging is supposed to always be relative to
a product.
Edits some views to add the default product in the context and makes the
field readonly if there is no `product_id` (that way, the user can't
no more create packaging without product).
Also, removes the domain in the action to display the packaging list
view so the user can see if there are some packagings without product
and can eventually delete them.
task-3076044
Part-of: odoo/odoo#109511
svs-odoo
0e71e350e3