Use sops for private key distribution

nixos/modules/borgbackup.nix

@@ -135,7 +135,11 @@ in {
       users.fsaccount.files = [
         {
           file = ".ssh/known_hosts";
-          parentDirectory = {mode = "u=rwx,g=,o=";};
+          parentDirectory = {
+            user = "fsaccount";
+            group = "users";
+            mode = "u=rwx,g=,o=";
+          };
         }
       ];
     };