Basic binary cache

Flake lock file updates:

• Updated input 'nix-index-database':
    'github:Mic92/nix-index-database/68ec961c51f48768f72d2bbdb396ce65a316677e' (2023-04-15)
  → 'github:Mic92/nix-index-database/e3e320b19c192f40a5b98e8776e3870df62dee8a' (2023-04-25)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/8dafae7c03d6aa8c2ae0a0612fbcb47e994e3fb8' (2023-04-22)
  → 'github:NixOS/nixpkgs/297187b30a19f147ef260abb5abd93b0706af238' (2023-04-30)

machines/storage/s0/default.nix

@@ -20,7 +20,10 @@
     openFirewall = true;
     secretKeyFile = "/run/agenix/binary-cache-private-key";
   };
-  age.secrets.binary-cache-private-key.file = ../../../secrets/binary-cache-private-key.age;
+  age.secrets.binary-cache-private-key = {
+    file = ../../../secrets/binary-cache-private-key.age;
+    owner = "nix-serve";
+  };
 
   services.iperf3.enable = true;
   services.iperf3.openFirewall = true;