🚀(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.

.sops.yaml

@@ -5,9 +5,11 @@ creation_rules:
   # - Anthony Le-Courric key-id: age1g5keveae6zhn059e7cxkjqdz4v3u47ypejv9ujld65nwh6d5pd9qfm0ecv
   # - Antoine Lebaud key-id: age12g6f5fse25tgrwweleh4jls3qs52hey2edh759smulwmk5lnzadslu2cp3
   # - Marie Pupo Jeammet key-id: age1tl80n23wq6zxegupwn70ew0yp225ua5v4dk800x7g2w6pvlxz46qk592pa
+  # - argocd key-id: age1qy04neuzwpasmvljqrcvhwnf0kz5cpyteze38c8avp0czewskasszv9pyw
   - age:
       age15fyxdwmg5mvldtqqus87xspuws2u0cpvwheehrtvkexj4tnsqqysw6re2x,
       age16hnlml8yv4ynwy0seer57g8qww075crd0g7nsundz3pj4wk7m3vqftszg7,
       age1g5keveae6zhn059e7cxkjqdz4v3u47ypejv9ujld65nwh6d5pd9qfm0ecv,
       age12g6f5fse25tgrwweleh4jls3qs52hey2edh759smulwmk5lnzadslu2cp3,
-      age1tl80n23wq6zxegupwn70ew0yp225ua5v4dk800x7g2w6pvlxz46qk592pa
+      age1tl80n23wq6zxegupwn70ew0yp225ua5v4dk800x7g2w6pvlxz46qk592pa,
+      age1qy04neuzwpasmvljqrcvhwnf0kz5cpyteze38c8avp0czewskasszv9pyw