staging: Use a static ssh host key

configuration/hardware-specific/vm.nix

@@ -16,6 +16,22 @@
     networkConfig.DHCP = "yes";
   };
 
+  # Both so we have a predictable key for the staging env, as well as
+  # to have a static key for decrypting the sops secrets for the
+  # staging env.
+  environment.etc."staging.key" = {
+    mode = "0400";
+    source = ../../keys/hosts/staging.key;
+  };
+
+  services.openssh.hostKeys = lib.mkForce [
+    {
+      type = "rsa";
+      bits = 4096;
+      path = "/etc/staging.key";
+    }
+  ];
+
   # # Set up VM settings to match real VPS
   # virtualisation.memorySize = 3941;
   # virtualisation.cores = 2;