[16] sale_order_type: don't depend in stock

[rafaelbn]

Hello,

We would like to use https://github.com/OCA/sale-workflow/tree/16.0/sale_order_type for services companies which don't use stock

Is this something acceptable for you or do we have to develop another separate module?

We would make your recommendations

Ping @oihane @pedrobaeza @rlizana @eLBati @carlosdauden @chienandalu @angelmoya @legalsylvain @igallart

I saw @hbrunn make a PR for 13 in #1603

@sbidoul recommendations in #1603 (comment)

Thank you!

@moduon MT-3778

[chienandalu]

Philosophically it should have been done many versions ago 😅 I guess it would been easier to do it in migration, but v17 is far in the horizon for now...

[hbrunn]

I've rebased my v13 PR to not conflict with the subsequent changes, should be simple(r) to cherry pick to later versions now