[FIX] sale_crm: create "customer" partner when converting leads to quotations

When creating a new partner on the fly at lead convert time we should created
a customer-oriented partner. This is done through the use of a specific
``res_partner_search_mode`` context key allowing to handle creation of a
partner flagged as "customer".

closes odoo/odoo#74593

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>