Registers the given schema (provided as a `dict`) to the given
        subject. Returns the id allocated to the schema in the registry.

def register_subject_version(self, subject, schema):
        """
        Registers the given schema (provided as a `dict`) to the given
        subject. Returns the id allocated to the schema in the registry.
        """
        data = json.dumps({'schema': json.dumps(schema)})
        res = requests.post(self._url('/subjects/{}/versions', subject), data=data, headers=HEADERS)
        raise_if_failed(res)
        return res.json()['id']