AKS: Expose WithHelm and WithDashboard on AzureKubernetesEnvironmentResource

## Problem
`WithHelm()` and `WithDashboard()` are available on the inner `KubernetesEnvironmentResource` but not exposed on `AzureKubernetesEnvironmentResource`. Users cannot configure Helm chart settings (namespace, release name, chart version) or dashboard settings from the AKS builder.

## Expected
```csharp
var aks = builder.AddAzureKubernetesEnvironment("aks")
.WithHelm(helm => helm.WithNamespace("my-ns").WithReleaseName("my-release"))
.WithDashboard();
```

## Related
Part of AKS hosting support (PR #16088)