System/Servenix: Add initial servenix system configuration

system/services/nginx-proxy-manager.nix

@@ -0,0 +1,36 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}: {
+  virtualisation.oci-containers.containers.nginx-proxy-manager = {
+    image = "jc21/nginx-proxy-manager:latest";
+    autoStart = true;
+
+    dependsOn = [
+      # "pihole"
+    ];
+
+    ports = [
+      "80:80"
+      # "81:81" # Web interface
+      "443:443"
+    ];
+
+    volumes = [
+      "nginx_config:/data"
+      "nginx_snippets:/snippets"
+      "nginx_letsencrypt:/etc/letsencrypt"
+    ];
+
+    environment = {
+      DISABLE_IPV6 = "true";
+    };
+
+    extraOptions = [
+      # "--net=host"
+      "--net=behind-nginx"
+    ];
+  };
+}