Persistency not reflected in Configuration

Not sure if this is a regression or new issue, but at least current release is affected.

Reproduce:
1. enable a persistent volume
2. experience issues like https://forum.xwiki.org/t/persistency-issue-xwiki-postgres-tomcat-on-kubernetes/13670 or https://forum.xwiki.org/t/permanent-directory-is-ignored-and-data-is-in-tomcat-work-directory/4095
3. cry

Workaround:

Explicitly pass `-Dxwiki.data.dir`, like so:

```
javaOpts:
  - "-Dxwiki.data.dir=/usr/local/xwiki/data"
```

Then most things seem to work on the surface.

The deployment is still far from immutable (stuff happens in the tomcat directory) and configurable (apparently most of the configuration is in the container, not any configmap), so I can not tell if this is everything one needs to do or if more places need to be touched.