* and stop setting default values in python operator code, so defaults can be set at the server side.

This issue is just for the PR and questions from maintainers. 
airflow/providers/yandex/hooks/yandex.py
'Will be used instead of OAuth token and SA JSON file path field if specified.',
            ),
            "extra__yandexcloud__service_account_json_path": StringField(
                lazy_gettext('Service account auth JSON file path'),
                widget=BS3TextFieldWidget(),
                description='Service account auth JSON file path. File content looks like '
                '{"id", "...", "service_account_id": "...", "private_key": "..."}. '
                'Will be used instead of OAuth token if specified.',
            ),
            "extra__yandexcloud__oauth": PasswordField(
                lazy_gettext('OAuth Token'),
                widget=BS3PasswordFieldWidget(),
                description='User account OAuth token. '
                'Either this or service account JSON must be specified.',
            ),
            "extra__yandexcloud__folder_id": StringField(
                lazy_gettext('Default folder ID'),
                widget=BS3TextFieldWidget(),
                description='Optional. This folder will be used '
                'to create all new clusters and nodes by default',
            ),
            "extra__yandexcloud__public_ssh_key": StringField(
                lazy_gettext('Public SSH key'),
                widget=BS3TextFieldWidget(),
                description='Optional. This key will be placed to all created Compute nodes'
                'to let you have a root shell there',
            ),
        }
    @staticmethod
    def get_ui_field_behaviour() -> Dict: