fix: extract duplicate config loading (#4242)

Also fix a problem with bin/cache-prune and FileCache and its enable_purge option

lib/config.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+$config = [];
+if (file_exists(__DIR__ . '/../config.ini.php')) {
+    $config = parse_ini_file(__DIR__ . '/../config.ini.php', true, INI_SCANNER_TYPED);
+    if (!$config) {
+        http_response_code(500);
+        exit("Error parsing config.ini.php\n");
+    }
+}
+Configuration::loadConfiguration($config, getenv());