Add Azure Service Bus upgrade guide for v5 to v6

Author: RyanThomasForge

menu/menu.yaml

@@ -832,6 +832,8 @@
         Title: Version 6 to 7
     - Title: Azure Service Bus
       Articles:
+      - Url: transports/upgrades/asbs-5to6
+        Title: Version 5 to 6
       - Url: transports/upgrades/asbs-4to5
         Title: Version 4 to 5
       - Url: transports/upgrades/asbs-3to4

transports/upgrades/asbs-5to6.md

@@ -0,0 +1,16 @@
+---
+title: Azure Service Bus Transport Upgrade Version 5 to 6
+summary: Migration instructions on how to upgrade the Azure Service Bus transport from version 5 to 6
+reviewed: 2025-09-18
+component: ASBS
+related:
+ - transports/azure-service-bus
+isUpgradeGuide: true
+upgradeGuideCoreVersions:
+ - 9
+ - 10
+---
+
+## Transport Encoding Header
+
+The `AzureServiceBusTransport.SendTransportEncodingHeader` API has been deprecated. The transport now relies on the [ContentType property](https://learn.microsoft.com/azure/service-bus-messaging/service-bus-messages-payloads#payload-serialization) of Azure Service Bus messages instead of a custom header. Remove any usage of this API.