[ReleasePR monitor] [Hub Generated] Review request for Microsoft.Insights to add version stable/2021-08-01 (#2035)

Create to sync Azure/azure-rest-api-specs#15845
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/monitor?expand=1)

Author: msftbot[bot]