backups: Add atomic backups with restic

configuration/services/conduit.nix

@@ -231,4 +231,14 @@ in {
       };
     };
   };
+
+  services.backups.conduit = {
+    user = "root";
+    paths = [
+      "/var/lib/private/matrix-conduit/"
+    ];
+    # Other services store their data in conduit, so no other services
+    # need to be shut down currently.
+    pauseServices = ["conduit.service"];
+  };
 }