Add machine-specific service configuration for WireGuard and related templates

Introduced a comprehensive guide for adding machine-specific services in the DEPLOYMENT-GUIDE.md, including steps to configure WireGuard for specific machines. Added example configuration files for boot settings, machine-specific configurations, and an example service for WireGuard. This enhances the modularity and flexibility of the NixOS deployment process, allowing for tailored configurations per machine.

config/example-machine/configuration.nix

@@ -0,0 +1,24 @@
+{ config, pkgs, ... }:
+
+{
+  # Import shared configuration and machine-specific modules
+  imports = [
+    # Import shared.nix with your domain parameter
+    # Replace "example.com" with your actual domain
+    (import /var/src/config-shared {
+      inherit config pkgs;
+      domain = "example.com";
+    })
+
+    # Import hardware-specific configuration
+    # This file is typically generated by nixos-generate-config
+    ./hardware-configuration.nix
+
+    # Import boot configuration (bootloader settings)
+    ./boot.nix
+
+    # Import any machine-specific services
+    # Comment out or remove if not needed
+    # ./example-service.nix
+  ];
+}