fix: Make attributes optional for RecordLog. (#202)

## Summary

The attributes parameter to RecordLog should have been optional.

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Author: kinyoklion

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

@@ -294,7 +294,7 @@ public static void RecordUpDownCounter(string name, long delta, IDictionary<stri
         /// <param name="message">the log message</param>
         /// <param name="level">the log level</param>
         /// <param name="attributes">any additional attributes to add to the log entry</param>
-        public static void RecordLog(string message, LogLevel level, IDictionary<string, object> attributes)
+        public static void RecordLog(string message, LogLevel level, IDictionary<string, object> attributes = null)
         {
             WithInstance(instance =>
             {