Investigate rclone config handling

Mackup backup hit a collision on ~/.config/rclone: the live directory is currently empty, while the existing backup store already contains rclone.conf.\n\nThis looks like a local/sensitive config case rather than a shared config case. We should decide whether Mackup should ignore rclone by default, support a local-only classification, or add special handling for credential-bearing config files.\n\nFor now, leave it unchanged.