[ReleasePR datamigration] Dev datamigration microsoft.data migration 2020 09 01 preview (#2150)

Create to sync Azure/azure-rest-api-specs#16032
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/datamigration?expand=1)

Author: msftbot[bot]