Support for unsubscribe groups

Issue:
If I want to import my customers, their email unsubscribe email preferences won't be observed. 

Is there any official support for syncing unsubscribe groups with firestore?

Desired solution: 

I would like to set values on my customer document that control which unsubscribe groups will be attached to the user. 

These preferences should be kept in sync with the data on sendgrid.


