Implement extraEnv pattern, support GitLab behind proxy

Original Issue

Using Latest Gitlab EE.

My kubernetes nodes are behind proxy and I need some globals to set proxy during helm install , so that Gitlab can communicate with outside world and clone repos afrom Gtihub.

thanks

Implementable work

Add the extraEnv patterns throughout the GitLab sub-charts, enabling the use of items like HTTP_PROXY, HTTPS_PROXY, and SOCKS_PROXY.

This is explicit, and supplemental to any functionality provided by PodPreset.

This can be done in such a way that we support direct value declarations, and thus complex methods including valueFrom via Secrets:

spec:
  containers:
  - name: example
    image: buysbox
    command: ["env"]
    env:
    - name: LOOKY
      value: "HERE"
    {{ if .Values.extraEnv -}}
    {{ toYaml .Values.extraEnv | nindent 4 }}
    {{- end }}
    volumeMounts:
    ...