Support encryption of user data

[mpoplavkov]

https://developer.apple.com/documentation/cloudkit/encrypting_user_data

[f-person]

This would be great because the encrypted fields would also be E2EE if Advanced Data Protection for iCloud is turned on.
Quoting the "Third-party app data" section of the iCloud data security overview:

Third-party app data stored in iCloud is always encrypted in transit and on server. When you turn on Advanced Data Protection, third-party app data stored in iCloud Backup and CloudKit encrypted fields and assets are end-to-end encrypted.