feat: allow tpl func in env for alpha init container

[t3mi]

Gives opportunity to refer to the chart internals if needed, .e.g. using the following input

alpha:
  initContainers:
    init:
      enabled: true
      env:
        - name: "RELEASE_NAME"
          value: "{{ .Release.Name }}"
        - name: "ZERO_SVC"
          value: "{{ template \"dgraph.zero.fullname\" . }}"

produces the output of

    initContainers:
      - name: release-name-dgraph-alpha-init
        image: docker.io/dgraph/dgraph:v23.0.1
        imagePullPolicy: "IfNotPresent"
        env:
          - name: RELEASE_NAME
            value: 'release-name'
          - name: ZERO_SVC
            value: 'release-name-dgraph-zero'

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