🚀(helm) prepare staging deployment

Thx @rouja for your help on deploying Desk. This commit slightly modifies
helm charts and helmfile to prepare the initial project deployment in a
staging environment.

@rouja updates:
- added secrets files for dev and staging environments (dev's one is empty)
- disable ingress by default, to avoid any security issue
- added an extra chart to benefit from Indie hoster Postgres operator

Thx to this commit we deployed a first draft version figured out
that the Django session were broken. We are using a cache session engine,
and wrongly configure cache backend to local memory. Thus, Django server
is not able to resolve the session, and enters in an infinite loop to
log-in the user.

src/helm/helmfile.yaml

@@ -5,7 +5,8 @@ repositories:
 
 releases:
   - name: postgres
-    namespace: desk
+    installed: {{ eq .Environment.Name "dev" | toYaml }}
+    namespace: {{ .Namespace }}
     chart: bitnami/postgresql
     version: 13.1.5
     values:
@@ -17,15 +18,27 @@ releases:
           enabled: true
           autoGenerated: true
 
+  - name: extra
+    installed: {{ ne .Environment.Name "dev" | toYaml }}
+    namespace: {{ .Namespace }}
+    chart: ./extra
+
   - name: desk
     version: {{ .Values.version }}
-    namespace: desk
+    namespace: {{ .Namespace }}
     chart: ./desk
     values:
-      - env.d/{{ .Environment.Name }}/values.desk.yaml
+      - env.d/{{ .Environment.Name }}/values.desk.yaml.gotmpl
+    secrets:
+      - env.d/{{ .Environment.Name }}/secrets.enc.yaml
 
 environments:
   dev:
     values:
       - version: 0.0.1
+  staging:
+    values:
+      - version: 0.0.1
+    secrets:
+      - env.d/{{ .Environment.Name }}/secrets.enc.yaml