[AzureMonitorExporter] remove Telemetry and EventSource messages from Console Output (Azure#38016)

* introduce environment variable to opt-in to DebugWriter. Off by default.

* remove environment variables. change to DEBUG only.

* cleanup

Author: Timothy Mothra

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Customizations/ApplicationInsightsRestClient.cs

@@ -89,14 +89,18 @@ internal HttpMessage CreateTrackRequest(IEnumerable<TelemetryItem> body)
                 content.WriteNewLine();
             }
 
+#if DEBUG
             TelemetryDebugWriter.WriteTelemetry(content);
+#endif
 
             return CreateRequest(RequestContent.Create(content.ToBytes()));
         }
 
         internal HttpMessage CreateTrackRequest(ReadOnlyMemory<byte> body)
         {
+#if DEBUG
             TelemetryDebugWriter.WriteTelemetryFromStorage(body);
+#endif
 
             return CreateRequest(RequestContent.Create(body));
         }

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Internals/Diagnostics/AzureMonitorExporterEventSource.cs

@@ -37,7 +37,9 @@ internal sealed class AzureMonitorExporterEventSource : EventSource
         internal const string EventSourceName = "OpenTelemetry-AzureMonitor-Exporter";
 
         internal static readonly AzureMonitorExporterEventSource Log = new AzureMonitorExporterEventSource();
+#if DEBUG
         internal static readonly AzureMonitorExporterEventListener Listener = new AzureMonitorExporterEventListener();
+#endif
 
         [NonEvent]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]