Feat/terminate contract endpoint

CHANGELOG:

### Added
- [#1135](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/1135) Add an API endpoint to terminate contracts

Related card: https://trello.com/c/mvTKjBYp/1749-nou-endpoint-per-baixa-de-contracte

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