feat: create DRF endpoint to get course index context

[navinkarkera]

Description

Continuing the work from #32856.

This PR adds DRF endpoint for fetching course index outline content and fixes issue mentioned here: #33667 (comment)

Useful information to include:

• Which edX user roles will this change impact? Developer, Content Authors

Supporting information

• feat: create DRF endpoint to get course index context #32856
• Private-ref: BB-8140

Testing instructions

• Get master devstack up and running.
• Start lms and cms using make {lms,cms}-up.
• Go to http://localhost:18010/api-docs/
• Scroll down till you find documentation for /contentstore/v1/course_index/{course_id} api.
• Use Try it out option to play around with the API.
• To make sure nothing has changed with normal cms course outline, visit any course outline page in studio.

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[connorhaugh]

I am not sure how to test whether this issue is resolved by moving the whole function call under bulk_operations.

One thing you could do is the following:
On a branch without these changes, create a unit test which counts the number of calls to mongo/mysql for this function, course_index and makes sure they are a specific number (say 30)
Then bring this unit test onto the branch with the changes, and make sure the unit test doesn't break.

Does that make sense? There are a couple of instances in edx-platform where we do this, I could find some for you if you like.

[navinkarkera]

@connorhaugh Thanks for the pointer. Have added a test which makes sure the number of calls to mysql and mongo same as before. Also, verified that moving get_course_index_context out of bulk context increases mongo calls to around 30.

[connorhaugh]

Sweet -- thanks for adding those tests, it dramatically boosts confidence re-merging this pr.
@KristinAoki can you merge this on monday (for on call purposes?)

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[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.