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.
This PR makes the optional type used configurable.

Fix coverage build.

Relates-To: NLAM-23
Signed-off-by: sopov <ext-alexander.sopov@here.com>

Author: asopov-here

olp-cpp-sdk-dataservice-read/include/olp/dataservice/read/DataRequest.h

@@ -167,7 +167,7 @@ class DATASERVICE_READ_API DataRequest final {
   template <class T>
   typename std::enable_if<
       std::is_same<T, boost::optional<std::string>>::value &&
-          std::is_same<T, porting::optional<std::string>>::value,
+          std::is_constructible<porting::optional<std::string>, T>::value,
       DataRequest&>::type
   WithBillingTag(porting::optional<std::string> tag) {
     billing_tag_ = std::move(tag);