support customizing envbox host files via `host_aliases`

a customer wants to set `host_aliases` in their envbox-based workspace. they mention this works for non-envbox workspaces. [K8s docs here](https://kubernetes.io/docs/tasks/network/customize-hosts-file-for-pods/#adding-additional-entries-with-hostaliases). below is what they've set in their template:

```terraform
spec {
restart_policy = "Never"

host_aliases {
hostnames = ["…."]
ip = "127.0.0.1"
}
```