Add output from https://github.com/NixIPFS/nixipfs-scripts/blob/6e3534430c2280be79e521ce489947a6ed17f451/nixipfs/src/mirror_tarballs.py#L138 to `DownloadFailed` then add this to https://github.com/NixIPFS/nixipfs-scripts/blob/6e3534430c2280be79e521ce489947a6ed17f451/nixipfs/src/mirror_tarballs.py#L119 finally dump this as JSON to https://github.com/NixIPFS/nixipfs-scripts/blob/6e3534430c2280be79e521ce489947a6ed17f451/nixipfs/src/mirror_tarballs.py#L209