[ReleasePR mysql] [Hub Generated] Review request for Microsoft.DBforMySQL to add version preview/2021-12-01-preview (#2427)

Create to sync Azure/azure-rest-api-specs#19454
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...azure-sdk:sdkAuto/mysql?expand=1)

Author: msftbot[bot]