Switched to contao-bundle.

composer.json

 {
     "name": "hhit/config-generator-bundle",
-    "type": "library",
+    "type": "contao-bundle",
     "license": "MIT",
     "authors": [
         {"name": "Hendrik Heneke", "email": "heneke@gmail.com"}
@@ -12,6 +12,7 @@
         "ext-ctype": "*",
         "ext-iconv": "*",
         "ext-json": "*",
+        "contao/core-bundle": "4.*",
         "paragonie/sodium_compat": "^1.14",
         "symfony/framework-bundle": "4.4.* || 5.2.*",
         "symfony/console": "4.4.* || 5.2.*",
@@ -20,9 +21,13 @@
         "zordius/lightncandy": "^1.2"
     },
     "require-dev": {
+        "contao/manager-plugin": "^2.0",
         "friendsofphp/php-cs-fixer": "^2.16",
         "phpunit/phpunit": "^9.5"
     },
+    "conflict": {
+        "contao/manager-plugin": "<2.0 || >=3.0"
+    },
     "config": {
         "optimize-autoloader": true,
         "preferred-install": {
@@ -43,7 +48,8 @@
     "extra": {
         "symfony": {
             "require": "4.4.* || 5.2.*"
-        }
+        },
+        "contao-manager-plugin": "HHIT\\ConfigGeneratorBundle\\ContaoManager\\ConfigGeneratorPlugin"
     },
     "bin": [
         "bin/cfgen"

src/ContaoManager/ConfigGeneratorPlugin.php

+<?php
+declare(strict_types=1);
+
+namespace HHIT\ConfigGeneratorBundle\ContaoManager;
+
+use Contao\ManagerPlugin\Bundle\BundlePluginInterface;
+use Contao\ManagerPlugin\Bundle\Config\BundleConfig;
+use Contao\ManagerPlugin\Bundle\Parser\ParserInterface;
+use HHIT\ConfigGeneratorBundle\ConfigGeneratorBundle;
+
+class ConfigGeneratorPlugin implements BundlePluginInterface
+{
+    public function getBundles(ParserInterface $parser)
+    {
+        return [BundleConfig::create(ConfigGeneratorBundle::class)];
+    }
+}