{AKS} az aks create: Add upcoming breaking change announcement (#31056)

Author: mbifeld

src/azure-cli/azure/cli/command_modules/acs/_breaking_change.py

@@ -0,0 +1,13 @@
+# --------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for license information.
+# --------
+
+from azure.cli.core.breaking_change import register_default_value_breaking_change
+
+register_default_value_breaking_change(
+    'aks create',
+    '--node-vm-size',
+    'Standard_DS2_V2 (Linux), Standard_DS2_V3 (Windows)',
+    'Dynamically Selected By Azure'
+)