Azure Container App Environment (ACA) with external container registry

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

Publish of a project with an external (non Azure) container registry fails:

```C#
#:package Aspire.Hosting.Azure.AppContainers@*
#:sdk Aspire.AppHost.Sdk@13.1.0
var builder = DistributedApplication.CreateBuilder(args);

#pragma warning disable ASPIRECOMPUTE003 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
var registry = builder.AddContainerRegistry("github", "ghcr.io");
var acaEnv = builder.AddAzureContainerAppEnvironment("test-env")
.WithContainerRegistry(registry);
#pragma warning restore ASPIRECOMPUTE003 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
```

```txt
$/aspire publish

✗ Failed to write Azure Bicep templates: The given key 'Aspire.Hosting.Azure.AzureContainerRegistryResource' was not present in the dictionary. (0.0s)
✗ [ERR] Failed to write Azure Bicep templates to [..]\aspire-output
✗ [ERR] Step 'publish-azuree7f9f' failed.
✗ Step 'publish-azuree7f9f' failed: The given key 'Aspire.Hosting.Azure.AzureContainerRegistryResource' was not present in the dictionary.
```

### Expected Behavior

- Using external container registry instead of Azure Container Registry is possible.
- Using public / no container registry instead of Azure Container Registry is possible.

### Steps To Reproduce

_No response_

### Exceptions (if any)

_No response_

### .NET Version info

```
$/aspire --version
13.1.0+8a4db1775c3fbae1c602022b636299cb04971fde
```txt

### Anything else?

```
$/aspire --version
13.1.0+8a4db1775c3fbae1c602022b636299cb04971fde
```txt