feat: add passed_timestamp to CourseGradeFactory for figures

[Waleed-Mujahid]

Description

This update passes passed_timestamp CourseGradeFactory so it can be used by figures. Previously we were querying PersistentCourseGrade which was a lot of unnecessary overhead. Since this code executes on every learner for every course for every site. that is a lot of queries we can avoid this way.

Legacy Figures changes

def course_grade(learner, course):
    """
    Compatibility function to retrieve course grades

    Returns the course grade for the specified learner and course
    """
    if RELEASE_LINE == 'ginkgo':
        course_grade = CourseGradeFactory().create(learner, course)
    else:  # Assume Hawthorn or greater
        course_grade = CourseGradeFactory().read(learner, course)

    persistent_course_grade = PersistentCourseGrade.objects.filter(user_id=learner.id, course_id=course.id).using(read_replica_or_default()).order_by('-modified').first()
    course_grade.passed_timestamp = persistent_course_grade.passed_timestamp if persistent_course_grade else None
    return course_grade
    

Note: Above code was not copied into develop-teak while rebasing which is why this issue was brought to our attention. This code is from KOA.

[Waleed-Mujahid]

@muhammadali286 @Anas-hameed I suggest we merge this change into koa as well and benchmark performance. Will look good in our metrics

[Anas-hameed]

LGTM