[Feat] Add extraVolumes/extraVolumeMounts to routerSpec for readOnlyRootFilesystem

[immanuel-peter]

Summary

Adds extraVolumes and extraVolumeMounts to routerSpec so the router pod can run with
readOnlyRootFilesystem: true.

Model containers already support writable mounts via servingEngineSpec.modelSpec[].extraVolumes / extraVolumeMounts, but the router deployment had no equivalent. Only containerSecurityContext was configurable. Without writable mounts for paths like /tmp and /home, enabling a read-only root filesystem on the router would fail at runtime.

FIX #966

Changes

• Add routerSpec.extraVolumes and routerSpec.extraVolumeMounts to values.yaml (default [])
• Render volume mounts and volumes in deployment-router.yaml
• Update values.schema.json and helm/README.md

Example

routerSpec:
  containerSecurityContext:
    readOnlyRootFilesystem: true
  extraVolumes:
    - name: tmp-volume
      emptyDir: {}
    - name: home-volume
      emptyDir: {}
  extraVolumeMounts:
    - name: tmp-volume
      mountPath: /tmp
    - name: home-volume
      mountPath: /home

---

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[gemini-code-assist]

Code Review

This pull request adds support for configuring additional volumes (extraVolumes) and volume mounts (extraVolumeMounts) for the router pod and container in the Helm chart, updating the deployment template, values schema, default values, and README documentation. A review comment suggests correcting the indentation of the commented-out examples in values.yaml to prevent invalid YAML syntax if a user uncomments them directly.

[gemini-code-assist]

The commented-out examples for extraVolumes and extraVolumeMounts are indented with extra spaces relative to their keys, and the keys are initialized with []. If a user uncomments these examples directly, it will result in invalid YAML because a block sequence cannot be nested under a flow sequence ([]).\n\nTo make it easier and safer for users to uncomment and use these examples, we should align the commented-out block items at the correct indentation level.

  # -- Additional volumes to add to the router pod, in Kubernetes volume format\n  extraVolumes: []\n  # - name: tmp-volume\n  #   emptyDir: {}\n  # - name: home-volume\n  #   emptyDir: {}\n  # -- Additional volume mounts to add to the router container, in Kubernetes volumeMount format\n  extraVolumeMounts: []\n  # - name: tmp-volume\n  #   mountPath: /tmp\n  # - name: home-volume\n  #   mountPath: /home

[ruizhang0101]

LGTM