d23cddd9e6
This is a BackupManifest schema change that will break recovering from any backups created before this change. However, considering that we haven't released this feature yet, I figured it wasn't worth the effort of doing a schema version bump or handling of the prior version. I'm making the field optional in the BackupManifest because in the event that we decide to backport the backup component to ESR 115, we need to handle the fact that ESR 115 has no notion of a profile group ID (and is unlikely to ever have such a notion). Differential Revision: https://phabricator.services.mozilla.com/D218976