Error on aspire publish when combining Kubernetes and NATS integrations

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

While building the apphost during execution of the publish command the NATS Hosting integration calls .WithArgs on the builder and passes a `ReferenceExpression` for the --user and --pass args:
https://github.com/dotnet/aspire/blob/5b92c02bcd205171118aa701ea905a073e61f24e/src/Aspire.Hosting.Nats/NatsBuilderExtensions.cs#L100
The Kubernetes Integration expects a string, which causes an exception while building:
https://github.com/dotnet/aspire/blob/5b92c02bcd205171118aa701ea905a073e61f24e/src/Aspire.Hosting.Kubernetes/KubernetesResource.cs#L282

### Expected Behavior

AddNats after AddKubernetesEnvironment does not cause an exception

### Steps To Reproduce

```
#:sdk Aspire.AppHost.Sdk@13.0.2
#:package Aspire.Hosting.Nats@13.0.2
#:package Aspire.Hosting.Kubernetes@13.0.2-preview.1.25603.5

var builder = DistributedApplication.CreateBuilder(args);
builder.AddKubernetesEnvironment("k8s");
builder.AddNats("nats");
builder.Build().Run();
```

### Exceptions (if any)

```
Unhandled exception. System.AggregateException: One or more errors occurred. (Command line
args must be strings)
---> System.NotSupportedException: Command line args must be strings
at
Aspire.Hosting.Kubernetes.KubernetesResource.ProcessArgumentsAsync(KubernetesEnvironmentCon
text environmentContext, DistributedApplicationExecutionContext executionContext,
CancellationToken cancellationToken) in
/_/src/Aspire.Hosting.Kubernetes/KubernetesResource.cs:line 285
```

### .NET Version info

.NET SDK:
Version: 10.0.100
Commit: b0f34d51fc
Workload version: 10.0.100-manifests.4c0ca8ba
MSBuild version: 18.0.2+b0f34d51f

### Anything else?

I assume the fix should be made on the Nats Hosting Integration side by converting the ReferenceExpression to a string.

Start with src/Aspire.Hosting.Nats/NatsBuilderExtensions.cs around line 100 and src/Aspire.Hosting.Kubernetes/KubernetesResource.cs around line 282. Reproduce the failure with AddKubernetesEnvironment followed by AddNats using the supplied sample, then verify that the publish/build path completes without the command-line-argument exception.

Written by the indexing model from the issue text.