[Storage] Make SignedResource not required in listSericeSAS

[blueww]

Description

SignedResource not required in listSericeSAS from server, so set is as not required in swagger/SDK.
Also add description to operation to fix swagger validate failure. (this failure not happen before, might cause by autorest upgrade)

Swagger pass review and merged in Azure/azure-rest-api-specs#3463

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• Please add REST spec PR link to the SDK PR
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[dsgouda]

Please bump the version number to 8.1.1

[dsgouda]

Please pull down the latest changes from psSdkJson6, run msbuild build.proj and regenerate the code

[dsgouda]

Since this is a non breaking change, please bump the version to 8.1.1-preview

[blueww]

@dsgouda

I have update the PR by rebase from psSdkJson6, and regenerate the code.
msbuild build.proj failed with following error. Do you know how to fix it?

c:\code\srpsdk\tools\bootstrapTools\bootstrap.targets(5,4): error : An exception occurred during a WebClient request.

I also upgrade to 8.1.1, but we won't release SRP SDK for this. will release with next new feature.

[dsgouda]

@blueww in case you are not planning to release this version please revert the version back to 8.1.0-preview
But please ensure you include these changes in the next PackageReleaseNotes

[blueww]

@dsgouda

I have reverted the version to 8.1.0

[dsgouda]

LGTM