chore: organise modules

Organise modules in a significantly better way with categories.

modules/services/ssh.nix

@@ -0,0 +1,27 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # Enable the OpenSSH daemon.
+  services.openssh = {
+    enable = true;
+    allowSFTP = true;
+    openFirewall = false;
+    authorizedKeysInHomedir = false;
+    settings = {
+      PermitRootLogin = "no";
+      PasswordAuthentication = false;
+      GatewayPorts = "no";
+    };
+  };
+
+  # add ssh key
+  users.users.nico.openssh.authorizedKeys.keys = [
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHzUJnqCpbRxggjyIZo4KWnTyHobPdi/xXkN1/n/yIMD"
+  ];
+
+  # enable ssh in the firewall
+  networking.firewall.allowedTCPPorts = [ 22 ];
+
+  # enable fail2ban
+  services.fail2ban.enable = true;
+}