feat: allow merge on extra env vars

[omidasadpour]

In fact, only list does not support merge. We agree that all list is rewritten as map， (list in k8s generally has a key called name, and this name can be used as the key of the map)

value.yaml before

# value.yaml 

env:
  - name: NODE_ENV
    value: production
  - name: PORT
    value: "3333"
  - name: SOME_SECRET
    valueFrom:
      secretKeyRef:
        key: SOME_SECRET
        name: some-secret

value.yaml after

# value.yaml

env:
  NODE_ENV:
    - name: NODE_ENV
      value: production
  PORT:
    - name: PORT
      value: "3333"
  SOME_SECRET:
    - name: SOME_SECRET
      valueFrom:
        secretKeyRef:
          key: SOME_SECRET
          name: some-secret

deployment.yaml

{{- with .Values.env }}
    env:
    {{- range $key, $value := . }}
    {{- toYaml $value | nindent 8 }}
    {{- end }}
{{- end }}

This will support the merge of list.

[endersonmaia]

I don't like the duplication of NODE_ENV in the following sample:

env:
  NODE_ENV:
    - name: NODE_ENV
      value: production

Also, if we wanna go that path, we'd need to update documentation, and since it's possible to merge env: also we could get rid of extraEnvVars.

But I'm still not convinced. 🤔

[omidasadpour]

I don't like the duplication of NODE_ENV in the following sample:

Me either. but the good news is it works in this way.

[omidasadpour]

I don't like the duplication of NODE_ENV in the following sample:

env:
  NODE_ENV:
    - name: NODE_ENV
      value: production

Also, if we wanna go that path, we'd need to update documentation, and since it's possible to merge env: also we could get rid of extraEnvVars.

But I'm still not convinced. 🤔

@endersonmaia
Helm treats lists as replacing the previous list, not merging them. In Kubernetes Helm charts, lists often represent an array of items, and Helm's default behavior is to replace the entire list with the new one from the values file.

One potential approach is to structure them as a map with unique keys for each item, and then merge these maps. (Like what I did in PR)

[endersonmaia]

This should be solved with #79