fix: allow converting envs from value to valueFrom

[samuelvl]

When kvisor is installed to read the cluster id from a configmap:

helm upgrade -i castai-kvisor ./charts/kvisor -n castai-agent \
  --set castai.clusterIdConfigMapKeyRef=castai-agent-metadata

The value is exposed as an environment variable using valueFrom:

- name: CLUSTER_ID
  valueFrom:
    configMapKeyRef:
      key: CLUSTER_ID
      name: castai-agent-metadata

If we now want to read the cluster id directly from a string we can do:

helm upgrade -i castai-kvisor ./charts/kvisor -n castai-agent \
  --set castai.clusterID=foo --reset-then-reuse-values

However this will fail because Helm can't apply valueFrom->value or value->valueFrom since the three-way merge keeps the existing setting and adds the new one, which is invalid (can't have both value and valueFrom defined):

Error: cannot patch "castai-kvisor-agent" with kind DaemonSet: DaemonSet.apps "castai-kvisor-agent" is invalid: spec.template.spec.containers[0].env[6].valueFrom: Invalid value: "": may not be specified when `value` is not empty && cannot patch "castai-kvisor-controller" with kind Deployment: Deployment.apps "castai-kvisor-controller" is invalid: spec.template.spec.containers[0].env[5].valueFrom: Invalid value: "": may not be specified when `value` is not empty

The fix is doing the same as in castai/helm-charts#1092