Add templating for env variables using valueFrom.

[nethi]

This is useful for scenarios like dealing with issue of "Failed to get final advertise address: No private IP address found, and explicit IP not provided". Weaviate troubleshooting documents to fix it using CIDR change, but this mayn't be feasible always.

As mentioned in this issue, the workaround of using CLUSTER_ADVERTISE_ADDR actually works. But we cannot use with this helm chart because values.yaml doesn't allow configuring it. This PR tries to fix it. There may be other use cases where this ability could help also

env:
  - name: CLUSTER_ADVERTISE_ADDR
    valueFrom:
      fieldRef:
        apiVersion: v1
        fieldPath: status.podIP

[weaviate-git-bot]

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