Add extraEnv config for the deployment pod

[consideRatio]

This extraEnv allow for configuration like:

extraEnv:
  - name: HELM_RELEASE_NAME
    value: "{{ .Release.Name }}"
  - name: JUPYTERHUB_API_TOKEN
    valueFrom:
      secretKeyRef:
        name: '{{ include "jupyterhub.hub.fullname" . }}'
        key: hub.services.binder.apiToken