Add fiber signal type parameter in fiber contracts

CHANGELOG:

### Added
- [#700](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/700) Add `fiber signal type` field in fiber contracts

Related card: https://trello.com/c/WBB1VYqN/1047-nou-camp-a-contractes-odoo-cobertura-fibra

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API created contract at local environment: