Function default_certificate_configuration_id_for_module 

fn default_certificate_configuration_id_for_module(
    configurations: &[CertificateConfigurationAndRequirements],
    course_module_id: Uuid,
) -> Option<Uuid>

The default certificate configuration a completion of this module alone earns.

configurations must come from crate::certificate_configurations::get_default_certificate_configurations_and_requirements_by_course, which has already dropped the configurations that require more than one module; a configuration merely naming this module among several is not one this module satisfies.