[Feature]: Give adequate response for Restore-AzApiManagement errors (compared to CLI)

### Description of the new feature

when I try restoring through Restore-AzApiManagement, I get:
```
Restore-AzApiManagement: ...restrore_from_backup.ps1:52:1
Line |
52 | Restore-AzApiManagement -ResourceGroupName $apiManagementResourceGrou …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| Long running operation failed with status 'BadRequest'.
```

when I do the same through az cli, Iget:
```
(RestoreFailed) Cannot restore: current SKU is 'StandardV2', backup SKU is 'Standard'
Code: RestoreFailed
Message: Cannot restore: current SKU is 'StandardV2', backup SKU is 'Standard'
```

### Proposed implementation details (optional)

the error from PowerShell should also give the message about: `Message: Cannot restore: current SKU is 'StandardV2', backup SKU is 'Standard'`.

Start by reproducing the Restore-AzApiManagement failure from restrore_from_backup.ps1 at line 52 and compare its output with the shown az CLI response. Trace the Restore-AzApiManagement entry point to find where the long-running operation error is surfaced. Done means PowerShell exposes the service's RestoreFailed message, including the SKU mismatch details.

Written by the indexing model from the issue text.