Add traces to emit telemetry initialization and heartbeat config (#316)

Author: xavierdecoster

src/NuGet.Services.Logging/ApplicationInsights.cs

@@ -40,8 +40,14 @@ private static void InitializeTelemetryConfiguration(string instrumentationKey,
                     if (heartbeatManager != null)
                     {
                         heartbeatManager.HeartbeatInterval = heartbeatInterval.Value;
+
+                        Trace.TraceInformation($"Telemetry initialized using configured heartbeat interval: {heartbeatInterval.Value}.");
                     }
                 }
+                else
+                {
+                    Trace.TraceInformation($"Telemetry initialized using default heartbeat interval.");
+                }
 
                 Initialized = true;
             }