MSUE-241: Store initial_device_ifv as device-only, non-syncing Keychain item

[apolwork]

Purpose

Fixes initial_device_ifv transfer between devices when restored from backup

Summary

• Disables storing initial_device_ifv into backup
• Updates initial_device_ifv attributes to store them in local keychain only

Testing

Device restored from backup (local or iCloud) should generate new initial_device_ifv

Checklist

• The change was thoroughly tested manually
• The change was covered with unit tests
• The change was tested with the integration example
• Necessary changes were made in the integration example (if applicable)
• New functionality is reflected in README (if applicable)