Function get_course_material_exercise

pub async fn get_course_material_exercise(
    conn: &mut PgConnection,
    user_id: Option<Uuid>,
    exercise_id: Uuid,
    fetch_service_info: impl Fn(Url) -> BoxFuture<'static, ModelResult<ExerciseServiceInfoApi>>,
) -> ModelResult<CourseMaterialExercise>