feat: add enterprise group deletion event

[jesperhodge]

Description:
When an EnterpriseGroup gets deleted, we want to send a message to the Openedx Event Bus that is read by enterprise-access to delete the corresponding PolicyGroupAssociation.

This is part of openedx/edx-enterprise#2434 .

This needs Kafka Event Bus setup from SRE to work, which has a related ticket. But without the SRE-side changes, this code isn't called, so this can just be deployed independently without breaking things.

Jira:
ENT-XXXX

Testing:
Setting this up would be a multiple day effort, but generally should work by running the new docker service that has been added here. See the unit tests and the attached video to confirm that this is working locally. Then do further

Merge checklist:

• ./manage.py makemigrations has been run
  • Note: This must be run if you modified any models.
    • It may or may not make a migration depending on exactly what you modified, but it should still be run.

Post merge:

• Ensure that your changes went out to the stage instance
• Deploy to prod instance

[jesperhodge]

Here's a video that shows the whole group deletion -> event bus message -> group association deletion cycle working locally on my machine. Don't try to set this up on your machine, it's too time consuming to set up.

Screen.Recording.2025-08-13.at.2.42.41.PM.mov