frontend: Terminal: Add ash shell support for Alpine containers

[illume]

Fixes #3941

Testing

Add an alpine container.

apiVersion: v1
kind: Pod
metadata:
  name: ash-only-pod
spec:
  containers:
    - name: alpine
      image: alpine
      command: ["/bin/ash", "-c", "while true; do sleep 30; done"]
  nodeSelector:
    kubernetes.io/os: linux

[k8s-ci-robot]

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