CodeGen from PR 16979 in Azure/azure-rest-api-specs

Utkarshjain/elastic (#16979)

* base api commit

* adding 2021-09-01-preview

* added 2021-10-01-preview

* updating readme files

* Fixing python readme

* Fixing readme

* Fixing readme

* Fixing readme

* adding elastic upgrade APIs

Co-authored-by: Utkarsh Jain <utkarshjain@microsoft.com>
Co-authored-by: pmp <pmp@microsoft.com>

Author: 3 people