Use std::optional if available.

Currently, SDK requires C++11 minimum.
So, boost::optional type is used for optional values.
For C++17 and above more convenient is to use std::optional instead.
The task NLAM-23 is about making this type configurable.
This commit is a second part of the task: olp-cpp-sdk-authentication.

Relates-To: NLAM-23
Signed-off-by: sopov <[email protected]>

Author: asopov-here

olp-cpp-sdk-authentication/include/olp/authentication/TokenResult.h

@@ -19,11 +19,11 @@
 
 #pragma once
 
-#include <olp/core/porting/optional.hpp>
 #include <chrono>
 #include <ctime>
 #include <string>
 
+#include <olp/core/porting/optional.hpp>
 #include "AuthenticationApi.h"
 #include "ErrorResponse.h"