Add ref parameter in partner search endpoint

CHANGELOG:

### Changed
- [#676](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/676) Require partner's `ref` parameter along with their NIF to be able to retrieve them from odoo through the "api/partner/search" endpoint.

Related card: https://trello.com/c/j1jUww9D/1056-identificaci%C3%B3-de-socis-per-contractaci%C3%B3-dapadrinats-nous

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curl -GET "http://odoo-sc.local:8069/api/partner/search?vat=ES07650352T&ref=1122" -H "API-KEY:xxx"