Allow OTRS formatted dates with change tariff API

CHANGELOG:

### Fix
- [#764](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/764) Allow OTRS formatted dates with change tariff API

Related card: https://trello.com/c/IdvbmDdf/1205-urgent-acceptar-data-de-canvi-de-tarifa-format-otrs

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