Adapt change tariff api endpoint to fiber contracts
CHANGELOG:
### Changed
- [#750](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/750) Adapt change tariff API's endpoint to work with both mobile and fiber contracts
Related card: https://trello.com/c/qvRw37sU/1174-modificaci%C3%B3-api-change-tariff
Edited by Pelayo García