Add OdooContractRefRelacionat to Change Tariff api
CHANGELOG:
### ADDED
- [#920](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/920) Add OdooContractRefRelacionat to Change Tariff api
Related card: https://trello.com/c/hXTXCzQ8/1431-vinculaci%C3%B3-contractes-amb-el-proc%C3%A9s-de-canvi-de-tarifa-de-m%C3%B2bil
Edited by César López Ramírez