WebServer: Move server configuration into WebServer::Configuration

This moves the configuration of the web server, which currently only
consists of the root path, into a new class, Configuration. Since the
configuration is global and not per client, it is accessed by a
singleton getter.

This change simplifies future extensions of the configurable parameters.

Userland/Services/WebServer/Configuration.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace WebServer {
+
+class Configuration {
+public:
+    Configuration(String root_path);
+
+    String const& root_path() const { return m_root_path; }
+
+    void set_root_path(String root_path) { m_root_path = move(root_path); }
+
+    static Configuration const& the();
+
+private:
+    String m_root_path;
+};
+
+}