Add a data migration to copy all course index data into MySQL

[bradenmacdonald]

Description

This is a follow up to #29058. This is the next step in moving part of the modulestore data (the course indexes / "active versions" table) from MongoDB to MySQL.

There are four steps planned in moving course index data to MySQL:

• Step 1: create the tables in MySQL, start writing to MySQL + MongoDB (done in Store split modulestore's course indexes in Django/MySQL (Take 2) #29058)
• Step 2: migrate all remaining courses to MySQL (this PR)
• Step 3: switch reads from MongoDB to MySQL
• Step 4 (much later, once we know this is working well): stop writing to MongoDB altogether.

Supporting information

An earlier version of this migration failed due to a case insensitivity issue, which has since been fixed (in #29058).

Testing instructions

1. Check out a master devstack. Make some changes to a course or two (maybe a library too).
2. At http://localhost:18000/admin/split_modulestore_django/splitmodulestorecourseindex/ verify that any courses that you've modified are already copied into MySQL. Keep this tab open.
3. Check out this PR and run LMS migrations
4. Open http://localhost:18000/admin/split_modulestore_django/splitmodulestorecourseindex/ in a new tab, and compare to the prior version. Courses that were already present in MySQL should be unchanged, and all remaining courses from your devstack should now be listed there.

Deadline

None

Other information

See also the ADR for Mongo removal.

[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald! I've created OSPR-6180 to keep track of it in JIRA.

As a core committer in this repo, you can merge this once the pull request is approved per the core committer reviewer requirements and according to the agreement with your edX Champion.

[edx-status-bot]

Your PR has finished running tests. There were no failures.

[natabene]

@bradenmacdonald Thank you for your contribution.

[ormsbee]

I'm going to be a bit busy today to watch this go out, but I'll merge on Monday morning.

[ormsbee]

@bradenmacdonald: FYI, there's a delay on this because I'm tracking down some flakiness added to the build that's related to the new table around active versions.

[bradenmacdonald]

@ormsbee Hmm ok, let me know if I can help.

[bradenmacdonald]

@ormsbee Just to confirm, it's a different issue than https://github.com/edx/edx-platform/pull/29109 right?

[ormsbee]

@bradenmacdonald: Yes, separate issue. I'll have a PR later this afternoon.

[openedx-webhooks]

@ormsbee, @kdmccormick: thought you might like to know that bradenmacdonald merged this pull request.

[openedx-webhooks]

@bradenmacdonald 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.

[edx-pipeline-bot]

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

[edx-pipeline-bot]

EdX Release Notice: This PR has been deployed to the production environment.

[edx-pipeline-bot]

EdX Release Notice: This PR has been deployed to the production environment.