Add new server modules and configurations for various services

- Introduced `default-creds` module for managing default credentials with Umami integration.
- Added `fail2ban` module for brute-force attack protection with configurable ban times.
- Created `firewall` module to enable and configure basic firewall settings.
- Implemented `gitea` module for self-hosted Git service with PostgreSQL backend.
- Developed `glance` module for a customizable dashboard with various widgets and themes.
- Added `iknowyou` module for a self-hosted password manager with production and demo environments.
- Introduced `kernel-hardening` module for enhancing kernel security settings.
- Created `mazanoke` module for a simple web application with Nginx integration.
- Added `mealie` module for a self-hosted meal planning application.
- Implemented `stirling-pdf` module for PDF generation service.
- Developed `umami` module for self-hosted analytics with secret management.
- Added `ssh` module for secure SSH configuration with user restrictions.
- Introduced `nixy` theme for a customized aesthetic experience across services.

hosts/server/variables.nix

@@ -0,0 +1,42 @@
+{
+  config,
+  lib,
+  ...
+}: {
+  imports = [
+    # Choose your theme here:
+    ../../themes/nixy.nix
+  ];
+
+  config.var = {
+    hostname = "jack";
+    username = "hadi";
+    configDirectory = "/home/" + config.var.username + "/.config/nixos"; # The path of the nixos configuration directory
+
+    keyboardLayout = "fr";
+
+    timeZone = "Europe/Paris";
+    defaultLocale = "en_US.UTF-8";
+    extraLocale = "fr_FR.UTF-8";
+
+    git = {
+      username = "Hadi";
+      email = "112569860+anotherhadi@users.noreply.github.com";
+    };
+
+    autoUpgrade = false;
+    autoGarbageCollector = true;
+
+    domain = "hadi.icu";
+    tunnelId = "a1dfa315-7fc3-4a65-8c02-8387932c35c3";
+    networkInterface = "enp3s0";
+  };
+
+  # Let this here
+  options = {
+    var = lib.mkOption {
+      type = lib.types.attrs;
+      default = {};
+    };
+  };
+}