Exams: Update import_edx_exam_grades to use MITx Online usernames

[briangrossman]

The import_edx_exam_grades management command should be updated to use usernames from MITx Online. Currently, import_edx_exam_grades assumes that it is provided with Micromasters usernames. It is currently possible, and in fact likely, that learners have different usernames on MITx Online, Micromasters, and edX.org. The import_edx_exam_grades needs to be updated to use MITx Online usernames.

import_edx_exam_grades currently takes a .csv file which contains usernames, grades, course_id's, and other fields.

Acceptance Criteria:

• [ ] Assume the usernames are MITx Online usernames. Get the learner's Micromasters username by looking up the learner's usersocialauth.uid for mitxonline.
• [ ] Add appropriate error messages for when we are unable to locate the learner's Micromaster's username

[asadiqbal08]

@briangrossman I got it. Do you have a sample .csv that I can take a look ?

[briangrossman]

@asadiqbal08 Here's a sample .csv DEDP_FALL_21_grades_adjusted091421_SAMPLE.csv