add default_code to mobile_contract_otrs_view

CHANGELOG:

### Added
- [#636](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/636) Add product_default_code to mobile_contract_otrs_view

Related card: https://trello.com/c/RCqWmXmZ/994-fer-una-crida-a-la-vista-sql-contract-mobile-un-cop-acabada-la-crida-a-mm-per-recuperar-la-tarifa-original

---