feat: add pre-delete signal

[navinkarkera]

Description

This is required in cases where we want to be able to delete or update database rows related to children blocks on the deleted block. Fetching children after deletion is not possible, which is why this signal is useful

Useful information to include:

• Which edX user roles will this change impact? "Developer"

Supporting information

• Related to: LTI XBlock Reusability Bug: Copy/Paste, Libraries, and Cross-Course Import Fail Due to DB-Stored Settings xblock-lti-consumer#594

Testing instructions

See PR: openedx/xblock-lti-consumer#627

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, @navinkarkera!

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

[feanil]

@navinkarkera can you rebase this and get the tests to green so we can get this reviewed.

[navinkarkera]

@feanil Done. Once the LTI xblock PR is merged, I can remove the temporary link to github branch and update this PR.

[navinkarkera]

TODO: Remove this before merging

[ormsbee]

I think this approach is fine. The only reason I'm not giving it an approval is because of the temporary requirements change pointing to a branch of the lti-consumer-block.

[navinkarkera]

@feanil This is ready to be merged.