Add client authentication code sample to Monitor Query README (#24311)

Author: scottaddie

sdk/monitor/Azure.Monitor.Query/README.md

@@ -32,6 +32,16 @@ dotnet add package Azure.Monitor.Query
 
 An authenticated client is required to query Logs or Metrics. To authenticate, create an instance of a [TokenCredential](https://docs.microsoft.com/dotnet/api/azure.core.tokencredential?view=azure-dotnet) class. Pass it to the constructor of your `LogsQueryClient` or `MetricsQueryClient` class.
 
+To authenticate, the following examples use `DefaultAzureCredential` from the [Azure.Identity](https://www.nuget.org/packages/Azure.Identity) package:
+
+```C# Snippet:CreateLogsClient
+var client = new LogsQueryClient(new DefaultAzureCredential());
+```
+
+```C# Snippet:CreateMetricsClient
+var metricsClient = new MetricsQueryClient(new DefaultAzureCredential());
+```
+
 ### Execute the query
 
 For examples of Logs and Metrics queries, see the [Examples](#examples) section.