helm: Support valueFrom by setting a dict value in zulip.environment.

This is possibly useful with both `SECRET_...`[^1] and
`SETTING_...`[^2][^3] values.

[^1]: https://kubernetes.io/docs/tasks/inject-data-application/distribute-credentials-secure/
[^2]: https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/
[^3]: https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/

Co-authored-by: Alex Vandiver <alexmv@zulip.com>

kubernetes/chart/zulip/README.md

@@ -144,6 +144,19 @@ variables are forwarded to the Docker container, you can read more about
 configuring Zulip through environment variables
 [here](https://github.com/zulip/docker-zulip/#configuration).
 
+Variables can be either a plain scalar value (i.e., a string or
+integer), or a projected value from a secret or configmap.  For
+example:
+
+```yaml
+SETTING_EXTERNAL_HOST: zulip.example.com
+SECRETS_email_password:
+  valueFrom:
+    secretKeyRef:
+      name: email
+      key: password
+```
+
 ### Dependencies
 
 The chart uses Memcached, RabbitMQ and Redis helm charts defined in

kubernetes/chart/zulip/templates/_helpers.tpl

@@ -90,6 +90,10 @@ include all env variables for Zulip pods
   value: "{{ .Values.zulip.password }}"
 {{- range $key, $value := .Values.zulip.environment }}
 - name: {{ $key }}
+  {{- if kindIs "map" $value }}
+  {{- toYaml $value | nindent 2 }}
+  {{- else }}
   value: {{ $value | quote }}
+  {{- end }}
 {{- end }}
 {{- end }}