feat: add course enrollment sink table

[Ian2012]

Description

This PR adds the base table for the course enrollment sink model. See https://github.com/openedx/platform-plugin-aspects/pull/64 for more information.

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[bmtcril]

I think this will be good once the platform-plungin-aspects version bumps are in, but I'd rather not merge it until we have a stable 1.0.x, which is hopefully today 🤞

[Ian2012]

@bmtcril friendly reminder of this one

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