env map value

[aogier]

Ciao, this PR exploits the possibilities of kubernetes to more richly express secrets in the environment by using secrets/configmap projections.
It is inobtrusive as it only mangle maps leaving any other value alone.

helm template zulip . \
  --set zulip.environment.SECRETS_email_password=password \
  --set-json zulip.environment.SECRETS_password='
    {"valueFrom":{"secretKeyRef":{"name": "secret", "key": "key"}}}' \
  -s templates/statefulset.yaml \
| yq -Y '.spec.template.spec.containers[] .env[] 
         | select((.name=="SETTING_EXTERNAL_HOST") 
                  or .name=="SECRETS_password")'

- name: SECRETS_email_password
  value: "password"
- name: SECRETS_password
  valueFrom:
    secretKeyRef:
      key: key
      name: secret

This easily unlocks the possibility to specify existing secrets in env vars without defining a dedicated one and going the #482 way. It does not breaks current workflow, but enable whoever want to do that to have it :)

Hope this helps, ciao!

[alexmv]

I did some rewording in the doc and commit message. Merged, and thanks @aogier!