Enable localhost as buld machine for hydra

hosts/hydra/configuration.nix

@@ -1,14 +1,37 @@
 { ... }:
 {
-  boot.loader.grub = {
+  boot = {
+    loader.grub = {
       enable = true;
       device = "/dev/vda";
     };
 
+    binfmt.emulatedSystems = [
+      "armv6l-linux"
+      "armv7l-linux"
+      "aarch64-linux"
+    ];
+  };
+
   networking = {
     hostName = "hydra";
     firewall.enable = false;
   };
 
+  nix = {
+    settings.allowed-uris = "http:// https://";
+    buildMachines = [
+      {
+        hostName = "localhost";
+        systems = [
+          "x86_64-linux"
+          "armv6l-linux"
+          "armv7l-linux"
+          "aarch64-linux"
+        ];
+      }
+    ];
+  };
+
   system.stateVersion = "23.05";
 }