Add debug log.

Author: kinyoklion

sdk/@launchdarkly/observability-dotnet/src/LaunchDarkly.Observability/Observe.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics;
 using System.Diagnostics.Metrics;
 using System.Threading;
+using LaunchDarkly.Observability.Logging;
 using Microsoft.Extensions.Logging;
 
 namespace LaunchDarkly.Observability
@@ -60,7 +61,7 @@ private static void WithInstance(Action<Instance> action)
             var instance = GetInstance();
             if (instance == null)
             {
-                // TODO: Log after PR with logger merged.
+                DebugLogger.DebugLog("Instance used before Observability Plugin initialized.");
                 return;
             }
 
@@ -101,7 +102,7 @@ public static void RecordException(Exception exception, IDictionary<string, obje
                 // Silently return if exception is null
                 return;
             }
-            
+
             WithInstance(instance =>
             {
                 var activity = Activity.Current;