Restore previous-service functionality in crm_lead api

CHANGELOG:

### Fixed
- [#850](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/850) Restore previous-service in crm_lead api

Related card: https://trello.com/c/BttP5R1u/1330-recuperar-el-previousservice-de-broadband-isp-info-des-de-formularis

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Depends on https://git.coopdevs.org/coopdevs/som-connexio/somoffice/-/merge_requests/144