[ReleasePR recoveryservicesbackup] [Hub Generated] Review request for Microsoft.RecoveryServices to add version stable/2021-08-01 (#1931)

Create to sync Azure/azure-rest-api-specs#15881
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/recoveryservicesbackup?expand=1)

Author: msftbot[bot]