[Feature]: Move `Disable-AzContextAutosave` into `Update-AzConfig` as an option

### Description of the new feature

Unify how to set options with Azure PowerShell; remove the cmdlet `Disable-AzContextAutosave` and move it into `Update-AzConfig` as an option.

### Proposed implementation details (optional)

```powershell
Update-AzConfig -EnableContextAutoSave <$true/$false>
```