Before this commit, the field opportunity_id was only visible in debug mode in
the sale.order form view. It was correctly pointing to opportunities but, when
used to create new records, it was creating leads instead.
The field is now always visible so users can link sale orders and opportunities
and a context was added so that the field correctly creates opportunities
instead of leads.
Task-3039802
closesodoo/odoo#104123
Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>