configurationmanager: add debug output signal

- adds signal that can be emitted to pass debug data to a client

Change-Id: I5023b8aec91b46acf08a52e6b046765ba4c4786a
Tuleap: #790

src/client/ring_signal.cpp

@@ -73,6 +73,8 @@ getSignalHandlers()
         exported_callback<DRing::ConfigurationSignal::GetHardwareAudioFormat>(),
         exported_callback<DRing::ConfigurationSignal::GetAppDataPath>(),
 #endif
+        /* Debug */
+        exported_callback<DRing::DebugSignal::MessageSend>(),
 
         /* Presence */
         exported_callback<DRing::PresenceSignal::NewServerSubscriptionRequest>(),

src/dring/configurationmanager_interface.h

@@ -268,4 +268,12 @@ struct ConfigurationSignal {
 #endif
 };
 
+// Can be used when a client's stdout is not available
+struct DebugSignal {
+    struct MessageSend {
+        constexpr static const char* name = "MessageSend";
+        using cb_type = void(const std::string&);
+    };
+};
+
 } // namespace DRing