Fix/ convert the previous owner vat to spanish VAT
CHANGELOG:
### Fixed
- [#506](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/506) Convert the service "previous_owner_vat_number" with an actual VAT format.
CHANGELOG:
### Fixed
- [#506](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/506) Convert the service "previous_owner_vat_number" with an actual VAT format.