[StorageAction] Added Accepted to StorageTask properties ProvisioningState

[blueww]

only a new value added to readonly enum, and doc change, so no test case update.

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[blueww]

Please don't merge it now, since we still need final confirmation from feature team.

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

Azure.ResourceManager.StorageActions