example:calculator: Add property overrides

Add examples of how to override the get and set property calls.

Change-Id: I1436ed7c286aa141ffb63a6af8c4766bf764f74b
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/example/calculator-client.cpp b/example/calculator-client.cpp
index 0ba1438..0c9b3ad 100644
--- a/example/calculator-client.cpp
+++ b/example/calculator-client.cpp
@@ -50,6 +50,15 @@
         std::cout << "Should be 1234: " << _ << std::endl;
     }
 
+    {
+        co_await c.owner("client");
+    }
+
+    {
+        auto _ = co_await c.owner();
+        std::cout << "Should be 'client': " << _ << std::endl;
+    }
+
     co_return;
 }