Expose health check information via "update status" API

[karencfv]

Once health check information is included in the inventory collection #9412 , we'll want to add a boolean to the "update status" API which determines whether the health checks have passed or not.

As health checks often fail during an update, we only want them visible via the external API when the system is idle or when an ongoing update has stalled for a set period of time. Perhaps 15-20 minutes?

See https://rfd.shared.oxide.computer/rfd/0612#_user_facing