Function headless_lms_server::domain::exercises::resolve_course_instance_or_exam_id_and_verify_that_user_can_submit

async fn resolve_course_instance_or_exam_id_and_verify_that_user_can_submit(
    conn: &mut PgConnection,
    user_id: Uuid,
    exercise: &Exercise,
    slide_id: Uuid
) -> Result<(CourseInstanceOrExamId, bool), ControllerError>

Submissions for exams are posted from course instances or from exams. Make respective validations while figuring out which.