Updating the error response class in Backup API Version 2021-01-01 (A…

…zure#12872)

* Updating the error response class in Backup API Version 2021-01-01

* Updating definition of CloudError

* Using ARM error class for ErrorDetail

* Copying NewErrorResponse as CloudError

* Updating CloudError object

* Marking properties as ReadOnly

* Added Error Description and AdditionalInfo

* Fixing Prettier issue

* Added object type for Error

* Updated error object description