[FC-0009] feat: Add subsection grading policy mismatch validation

[yusuf-musleh]

Description

This implements openedx/modular-learning#20, it adds validation for the grading assignment and grading policy in subsections, showing a warning in Studio if there is a mismatch.

Testing instructions

1. Login to Studio: http://localhost:18010/
2. Click on an existing course or create a new one
3. Navigate to the Grading Settings of the selected course: eg: http://localhost:18010/settings/grading/<course_key>
4. Create a new Assignment Type by click on "+ New Assignment Type"
   1. Give it a name and weight
   2. Save
5. Navigate back to the Course Outline page in Studio: http://localhost:18010/course/<course_key>
6. Click configure on a Subsection and select the newly created Grading Assignment type from the "Grade as" dropdown menu in the Subsection Settings modal, and save it
7. After the change is reflected, navigate back to the Grading Settings http://localhost:18010/settings/grading/<course_key>
   1. Delete the newly created Grading Assignment Type
   2. Save
8. Navigate back to the Course Outline page you should see a warning message under the subsection that looks like this:
   

---

Private ref: FAL-3464

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[mphilbrick211]

Hi @yusuf-musleh! Is this ready for review?

[bradenmacdonald]

@mphilbrick211 This is part of FC-0009 actually, and I can review it.

[yusuf-musleh]

@mphilbrick211 @bradenmacdonald yes, its ready for review.

[bradenmacdonald]

👍 Thanks! Nice work. I just had one question but this is good to go.

• I tested this: in Studio, as described
• I read through the code
• I checked for accessibility issues
• Includes documentation: n/a

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX staging environment in preparation for a release to production.

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX production environment.

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX staging environment in preparation for a release to production.