Update postgres helm chart to latest version

We didn't upgrade postgres in ~1,5y and are now facing 2 major version upgrade:

-  version: 8.6.4                                                                           
+  version: 10.9.1

See https://github.com/bitnami/charts/tree/master/bitnami/postgresql#upgrading for a summary of breaking changes.

Imo we should do this ASAP before we get more users.

I already tried upgrading in !41 (merged) but hit this and reverted:

Last Helm logs:

Looks like there are no changes for Service "nc-rabbitmq-headless"
Looks like there are no changes for Service "nc-redis-headless"
Looks like there are no changes for Service "nc-redis-master"
error updating the resource "nc-postgresql":
   cannot patch "nc-postgresql" with kind StatefulSet: StatefulSet.apps "nc-postgresql" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', and 'updateStrategy' are forbidden
warning: Upgrade "nc" failed: cannot patch "nc-postgresql" with kind StatefulSet: StatefulSet.apps "nc-postgresql" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', and 'updateStrategy' are forbidden
  Normal  error  39s  helm-controller  reconciliation failed: Helm upgrade failed: cannot patch "nc-postgresql" with kind StatefulSet: StatefulSet.apps "nc-postgresql" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', and 'updateStrategy' are forbidden
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information