Machine-readable restore status

We have a --json flag for getting machine-readable status for a backup. When we're getting restore status from fdbrestore, we don't have this option. A JSON option would be helpful when we are working with restores from the Kubernetes operator or from other tooling, so that we could programmatically check whether the restore has completed.

Start by locating the fdbrestore status entry point and the existing --json implementation for backup status. Compare their output paths and determine the restore status fields that tooling needs. Done means fdbrestore can emit machine-readable restore status, including whether the restore has completed, for Kubernetes and other tooling.

Written by the indexing model from the issue text.