[Storage] Add warning message for AllowBlobPublicAccess default behavior change (#20679)

* Add warning for AllowBlobPublicAccess default behavior change

* add changelog

* update message

* Update warning message

---------

Co-authored-by: Yeming Liu <[email protected]>

Author: yifanz0

src/Storage/Storage.Management/ChangeLog.md

@@ -18,6 +18,8 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Add a warning message for the upcoming breaking change when creating a Storage account
+    - `New-AzStorageAccount`
 * Removed the ValidateSet of StandardBlobTier parameter
     - `Copy-AzStorageBlob`
     - `Set-AzStorageBlobContent` 

src/Storage/Storage.Management/StorageAccount/NewAzureStorageAccount.cs

@@ -22,9 +22,14 @@
 using Microsoft.Azure.Commands.ResourceManager.Common.ArgumentCompleters;
 using System;
 using System.Collections.Generic;
+using Microsoft.WindowsAzure.Commands.Common.CustomAttributes;
 
 namespace Microsoft.Azure.Commands.Management.Storage
 {
+    [GenericBreakingChange("Default value of AllowBlobPublicAccess will be changed from True to False in a future release. " +
+        "When AllowBlobPublicAccess is False on a storage account, it is not permitted to configure container ACLs to allow anonymous access to blobs within the storage account.", 
+        OldWay = "AllowBlobPublicAccess is set to True by defult.", 
+        NewWay = "AllowBlobPublicAccess is set to False by default.")]
     [Cmdlet("New", ResourceManager.Common.AzureRMConstants.AzureRMPrefix + "StorageAccount", DefaultParameterSetName = AzureActiveDirectoryDomainServicesForFileParameterSet), OutputType(typeof(PSStorageAccount))]
     public class NewAzureStorageAccountCommand : StorageAccountBaseCmdlet
     {