Add EventGridSystemTopicEventSubscription with deadletter not working

### Description

I want to create an event subscription for a FunctionApp on a SystemTopic but can not find how to define the DeadletterEndpoint. My pipeline has Az module v12.5.0 installed.

The following code is working but how can I define the storage account container for deadletter?

```
$funcid = "/subscriptions/$funcSubID/resourceGroups/$func_rg/providers/Microsoft.Web/sites/$funcapp/functions/$func_name" $func_evdo = New-AzEventGridAzureFunctionEventSubscriptionDestinationObject -ResourceId $funcid

New-AzEventGridSystemTopicEventSubscription -ResourceGroupName $resourceGroupName `   
-eventSubscriptionName $eventSubscriptionName `
-systemTopicName $systemTopicName `
-destination $func_evdo
```
I searched this documentation but couldn't find something about DeadletterEndpoint or destination: https://learn.microsoft.com/en-us/powershell/module/az.eventgrid/new-azeventgridsystemtopiceventsubscription?view=azps-12.5.0

### Script or Debug output

```PowerShell
The parameter cannot be found that matches name - I tried DeadletterEndpoint or DeadletterDestination
```

### Environment data

```PowerShell
PSVersion: 7.4.6
```

### Module versions

```PowerShell
Az.Accounts: 4.0.0
Az.EventGrid: 2.1.0
```

### Error output

```PowerShell

```

Start with the New-AzEventGridSystemTopicEventSubscription cmdlet and its linked Az.EventGrid 2.1.0 documentation, checking the available destination and dead-letter parameters. Compare the documented interface with the reported command behavior and confirm that a storage account container can be configured; done means the supported configuration is exposed or the documentation clearly explains the limitation.

Written by the indexing model from the issue text.