detach PIHTTPServer::Endpoint to base struct PIHTTP::ServerEndpoint (private header), no functionality changes in HTTP server

Ready to implement this private base struct to MQTT client

libs/main/http_common/pihttptypes.h

@@ -210,6 +210,11 @@ public:
 PIP_EXPORT const char * methodName(Method m);
 
 
+//! \~english Request handler used by registered routes and fallback processing.
+//! \~russian Обработчик запроса, используемый зарегистрированными маршрутами и fallback-обработкой.
+using RequestFunction = std::function<PIHTTP::MessageMutable(const PIHTTP::MessageConst &)>;
+
+
 }; // namespace PIHTTP