[CppRest] Support optional parameters (#6959)

* Use boost::optional for parameters that are not required.

* Update sample petstore client.

samples/client/petstore/cpprest/api/StoreApi.h

@@ -26,6 +26,8 @@
 #include <map>
 #include <cpprest/details/basic_types.h>
 
+#include <boost/optional.hpp>
+
 namespace io {
 namespace swagger {
 namespace client {
@@ -45,15 +47,17 @@ public:
     /// For valid response try integer IDs with value &lt; 1000. Anything above 1000 or nonintegers will generate API errors
     /// </remarks>
     /// <param name="orderId">ID of the order that needs to be deleted</param>
-    pplx::task<void> deleteOrder(utility::string_t orderId);
+    pplx::task<void> deleteOrder(
+        utility::string_t orderId
+    );
     /// <summary>
     /// Returns pet inventories by status
     /// </summary>
     /// <remarks>
     /// Returns a map of status codes to quantities
     /// </remarks>
-    
-    pplx::task<std::map<utility::string_t, int32_t>> getInventory();
+    pplx::task<std::map<utility::string_t, int32_t>> getInventory(
+    );
     /// <summary>
     /// Find purchase order by ID
     /// </summary>
@@ -61,7 +65,9 @@ public:
     /// For valid response try integer IDs with value &lt;&#x3D; 5 or &gt; 10. Other values will generated exceptions
     /// </remarks>
     /// <param name="orderId">ID of pet that needs to be fetched</param>
-    pplx::task<std::shared_ptr<Order>> getOrderById(int64_t orderId);
+    pplx::task<std::shared_ptr<Order>> getOrderById(
+        int64_t orderId
+    );
     /// <summary>
     /// Place an order for a pet
     /// </summary>
@@ -69,7 +75,9 @@ public:
     /// 
     /// </remarks>
     /// <param name="body">order placed for purchasing the pet</param>
-    pplx::task<std::shared_ptr<Order>> placeOrder(std::shared_ptr<Order> body);
+    pplx::task<std::shared_ptr<Order>> placeOrder(
+        std::shared_ptr<Order> body
+    );
 
 protected:
     std::shared_ptr<ApiClient> m_ApiClient;