add options to allow backing up to specific machine

backup-target.nix

@@ -0,0 +1,15 @@
+# configuration allowing this machine to be user as a backup server
+{ config, lib, pkgs, ... }:
+
+{
+  users.users.backup = {
+    isNormalUser = true;
+    openssh.authorizedKeys.keys = [
+    ''command="${pkgs.rrsync}/bin/rrsync /mnt/backup/",restrict sh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIF1e7hxxQD7pVKMquEuiBrLNFfx9ZRAOU1SGky4iXacD Ithuriel@openmediavault''
+    ];
+
+    packages = [
+      pkgs.rsync
+    ];
+  };
+}