[Storage] Support allowProtectedAppendWrites in ImmutabilityPolicy

[blueww]

Description

The design already pass review in https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/497

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
  • the markdown help files have been regenerated using the commands listed here

[blueww]

I see static analysis report a breaking change:

"Microsoft.Azure.PowerShell.Cmdlets.Storage.Management.dll","Microsoft.Azure.Commands.Management.Storage.SetAzureStorageContainerImmutabilityPolicyCommand","Set-AzRmStorageContainerImmutabilityPolicy","0","1050","The parameter set '__AllParameterSets' for cmdlet 'Set-AzRmStorageContainerImmutabilityPolicy' has been removed.","Add parameter set '__AllParameterSets' back to cmdlet 'Set-AzRmStorageContainerImmutabilityPolicy'."

What does '__AllParameterSets' means, we don't have a parameter set with this name?
I added it to exception, but not sure why this is breaking.
Hope it won't block this feature adding to PSH stable release.