Userland: Add support for jails

This happens in two ways:
1. LibCore now has two new methods for creating Jails and attaching
   processes to a Jail.
2. We introduce 3 new utilities - lsjails, jail-create and jails-attach,
   which list jails, create jails and attach processes to a Jail,
   respectively.

Userland/Utilities/lsjails.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <LibCore/Stream.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments)
+{
+    TRY(Core::System::pledge("stdio rpath"));
+    TRY(Core::System::unveil("/sys/kernel/jails", "r"));
+    TRY(Core::System::unveil(nullptr, nullptr));
+
+    auto jails_data = TRY(Core::Stream::File::open("/sys/kernel/jails"sv, Core::Stream::OpenMode::Read));
+
+    TRY(Core::System::pledge("stdio"));
+
+    outln("Index    Name");
+    auto file_contents = TRY(jails_data->read_all());
+    auto json = TRY(JsonValue::from_string(file_contents));
+    json.as_array().for_each([](auto& value) {
+        auto& jail = value.as_object();
+        auto index = jail.get("index"sv).to_string();
+        auto name = jail.get("name"sv).to_string();
+
+        outln("{:4}     {:10}", index, name);
+    });
+
+    return 0;
+}