[Samples] Messaging docs fixes (Azure#58508)

The focus of these changes is to fix stale docs
 after Service Bus sample centralization (Azure#58506)

 - Added "Application samples" section to the Service Bus samples index
   with links to the centralized dead-letter-queue, topic-filters, and
   plugin-sample projects

 - Updated .NET version references from 5.0 to 10.0 in dead-letter-queue
   and topic-filters READMEs

Author: jsquire

samples/servicebus/dead-letter-queue/README.md

@@ -47,7 +47,7 @@ In order to run the sample, you will need a Service Bus Namespace. For more info
 
 To build the sample:
 
-1. Install [.NET 5.0](https://dot.net) or newer.
+1. Install [.NET 10.0](https://dotnet.microsoft.com/download) or newer.
 
 2. Run in the project directory:
 

samples/servicebus/topic-filters/README.md

@@ -39,7 +39,7 @@ In order to run the sample, you will need a Service Bus Namespace. For more info
 
 To build the sample:
 
-1. Install [.NET 5.0](https://dot.net) or newer.
+1. Install [.NET 10.0](https://dotnet.microsoft.com/download) or newer.
 
 2. Run in the project directory:
 

sdk/servicebus/Azure.Messaging.ServiceBus/samples/README.md

@@ -32,3 +32,11 @@ description: Samples for the Azure.Messaging.ServiceBus client library
 - [Long-running processing](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/servicebus/Azure.Messaging.ServiceBus/samples/Sample18_LongRunningProcessing.md)
 - [Distributed tracing and monitoring](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/servicebus/Azure.Messaging.ServiceBus/samples/Sample19_DistributedTracing.md)
 - [Performance patterns](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/servicebus/Azure.Messaging.ServiceBus/samples/Sample20_PerformancePatterns.md)
+
+## Application samples
+
+These samples demonstrate end-to-end application scenarios using Azure Service Bus.
+
+- [Dead-letter queues](https://github.com/Azure/azure-sdk-for-net/blob/main/samples/servicebus/dead-letter-queue/README.md)
+- [Topic filters](https://github.com/Azure/azure-sdk-for-net/blob/main/samples/servicebus/topic-filters/README.md)
+- [Plugin extensibility pattern](https://github.com/Azure/azure-sdk-for-net/blob/main/samples/servicebus/plugin-sample/README.md)