feat: add course enrollment sink

[Ian2012]

Description

This PR creates a sink for the Course Enrollment mode. It uses the ENROLL_STATUS_CHANGE signal to listen for changes in enrollments.

Testing instructions

1. Check out this branch on your local repository.
2. Run Aspects migrations to create the necessary table.
3. Enable the course enrollment sink waffle flag event_sink_clickhouse.course_enrollment.enabled.
4. Enroll/unenroll in a course via the courseware page or in the instructor dashboard.
5. Verify a record is stored for the enrollment.
6. Verify the dump_data_to_clickhouse can dump old data.

Merge checklist:
Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
platform_plugin_aspects
__init__.py
signals.py
platform_plugin_aspects/sinks
__init__.py
course_enrollment_sink.py
serializers.py					208
Project Total

This report was generated by python-coverage-comment-action

[saraburns1]

@Ian2012 - i enrolled/unenrolled and also ran the dump to clickhouse. It looks like the ID values are not unique, is that expected?

Also, it doesn't seem to differentiate between enroll and unenroll, do we need that info?

[Ian2012]

@saraburns1 Yes, the IDs correspond to the record on the DB and it's expected to be duplicated. We will create an MV that stores the last records per learner per course and their status. Tracking logs will be available for historical records. This will only be used to backfill data from the enrollments and know their last state. I think we can calculate enroll/unenroll with the is_active key

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