refactor: Clio Config (#1544)

Implementation of new config definition + methods + UT

Steps that still need to be implemented: 
- Make ClioConfigDefinition and it's method to be as constexpr as
possible
- Getting User Config file and populating the values in ConfigDefinition
while checking for constraints on user values
- Replacing all the places where we fetch config values (by using
config.valueOr/MaybeValue) to instead get it from Config Definition
- Generate markdown file using Clio Config Description

tests/unit/util/newconfig/ConfigValueTests.cpp

@@ -0,0 +1,40 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "util/newconfig/ConfigValue.hpp"
+
+#include <gtest/gtest.h>
+
+using namespace util::config;
+
+TEST(ConfigValue, testConfigValue)
+{
+    auto cvStr = ConfigValue{ConfigType::String}.defaultValue("12345");
+    EXPECT_EQ(cvStr.type(), ConfigType::String);
+    EXPECT_TRUE(cvStr.hasValue());
+    EXPECT_FALSE(cvStr.isOptional());
+
+    auto cvInt = ConfigValue{ConfigType::Integer}.defaultValue(543);
+    EXPECT_EQ(cvInt.type(), ConfigType::Integer);
+    EXPECT_TRUE(cvStr.hasValue());
+    EXPECT_FALSE(cvStr.isOptional());
+
+    auto cvOpt = ConfigValue{ConfigType::Integer}.optional();
+    EXPECT_TRUE(cvOpt.isOptional());
+}