[iOS] Add iCloud sync for session duration
Consider a CloudKit solution for backing up / syncing session-start timestamp and session duration.
Major concern: this work takes data that previously only existed on the user’s device, and puts it in the cloud.
- Encrypt the data
- Be very explicit about what’s synced to iCloud
- Opt-in by default
- Give user full access to view data that’s being synced
- Give user full access to remove data from iCloud