Permanently fixes https://github.com/twentyhq/private-issues/issues/389 On a non-nullable select field, default value should not be removable, otherwise users won't be able to create new records from the interface. This PR enforces this in FE and BE. https://github.com/user-attachments/assets/1dfa2bcc-b9df-4a00-9915-679d36ec1b25