feat: enable authoring MFE markdown editor waffle flag for everyone by default

[Anas12091101]

Description

This PR replaces the contentstore.use_react_markdown_editor flag with contentstore.disable_react_markdown_editor to enable the Markdown editor by default for all courses. The editor will now be disabled only if the contentstore.disable_react_markdown_editor flag is explicitly turned on.

Useful information to include:

• Which edX user roles will this change impact? Common user roles are "Course Author" & "Developer"
• Include screenshots for changes to the UI (ideally, both "before" and "after" screenshots, if applicable).
• Provide links to the description of corresponding configuration changes. Remember to correctly annotate these
  changes.

Supporting information

Link to other information about the change, such as Jira issues, GitHub issues, or Discourse discussions.
Be sure to check they are publicly readable, or if not, repeat the information here.

Relevant PRs: #36512, openedx/frontend-app-authoring#1805

Testing instructions

Please provide detailed step-by-step instructions for testing this change.

• Visit http://{CMS_BASE_URL}/api/contentstore/v1/course_waffle_flags/{course_id} in your browser and confirm that the use_react_markdown_editor value is True.
• Add a Waffle Flag Course Override for flag contentstore.disable_react_markdown_editor for a course and Force On` the override choice.
• Visit http://{LMS_BASE_URL}/api/contentstore/v1/course_waffle_flags/{course_id} in your browser and confirm that the flag’s value is False.

Deadline

"None" if there's no rush, or provide a specific date or event (and reason) if there is one.

Other information

Include anything else that will help reviewers and consumers understand the change.

• Does this change depend on other changes elsewhere?
• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.
• If your database migration can't be rolled back easily.

[openedx-webhooks]

Thanks for the pull request, @Anas12091101!

This repository is currently maintained by @openedx/wg-maintenance-edx-platform.

Once you've gone through the following steps feel free to tag them in a comment and let them know that your changes are ready for engineering review.

🔘 Get product approval

If you haven't already, check this list to see if your contribution needs to go through the product review process.

• If it does, you'll need to submit a product proposal for your contribution, and have it reviewed by the Product Working Group.
  • This process (including the steps you'll need to take) is documented here.
• If it doesn't, simply proceed with the next step.

🔘 Provide context

To help your reviewers and other members of the community understand the purpose and larger context of your changes, feel free to add as much of the following information to the PR description as you can:

• Dependencies

  This PR must be merged before / after / at the same time as ...

• Blockers

  This PR is waiting for OEP-1234 to be accepted.

• Timeline information

  This PR must be merged by XX date because ...

• Partner information

  This is for a course on edx.org.

• Supporting documentation
• Relevant Open edX discussion forum threads

🔘 Get a green build

If one or more checks are failing, continue working on your changes until this is no longer the case and your build turns green.

Details

---

Where can I find more information?

If you'd like to get more details on all aspects of the review process for open source pull requests (OSPRs), check out the following resources:

• Overview of Review Process for Community Contributions
• Pull Request Status Guide
• Making changes to your pull request

When can I expect my changes to be merged?

Our goal is to get community contributions seen and reviewed as efficiently as possible.

However, the amount of time that it takes to review and merge a PR can vary significantly based on factors such as:

• The size and impact of the changes that it introduces
• The need for product review
• Maintenance status of the parent repository

💡 As a result it may take up to several weeks or months to complete a review and merge your PR.

[Anas12091101]

@kdmccormick Could you please take a look at this PR when you get a chance?

[kdmccormick]

A couple minor code comments, looks good otherwise.

However, I am hesitant to release the Markdown editor as default-on without having performed acceptance testing yet. Could we wait until some initial testing is performed, and then make a judgement call about when to merge this PR?

FYI @pdpinch @jmakowski1123

[pdpinch]

I think this is ready to be merged after a rebase. @kdmccormick let me know if you disagree.

@Anas12091101 I think we'd like a backport to the realease/teak.master branch as well.

[pdpinch]

@Anas12091101 can you rebase this?

@kdmccormick do you feel this is blocked by openedx/frontend-app-authoring#1920 or can we consider that an enhancement?

[kdmccormick]

An update on this... using the same approach as this PR, we flipped the Studio MFE waffle flags to by on by-default back in April, and actually regretted taking approach. It ended up being a lot of work for us developers, and a lot of work for operators who wanted to continue temporarily disabling the flags. 2U ended up having to update 100+ flags in their database, and I fear that other operators will have to do the same. Furthermore, due to how Waffle works, the change removed the ability for the MFE pages to be released to certain set of beta users.

We discussed this in Maintenance Working Group and decided that your original approach @Anas12091101 (the one where you use a migration to turn the flags on) is superior, and that we'd like to try using that approach going forward for turning on waffle flags by default.

I'm still not sure if we are merging this PR for Teak or for Ulmo, but in either case, could you revert back to the original migration-based approach you had? Thanks, and sorry for the extra work!

[kdmccormick]

OK, we have consensus that we should turn this on by default in Teak! Thanks for your patience @Anas12091101 . Would you be able to update the PR based on my latest feedback, and then once we merge this, open a backport against release/teak?

[kdmccormick]

Just due to the tight timeline, I'm recreating Anas's first commit in a new PR over here: #36872