print fresh install steps on `helm uninstall` for any app using cas-postgres' wal-g

Otherwise patroni gets confused, and throws an error:
```
CRITICAL: system ID mismatch, node cas-ggircs-patroni-1 belongs to a different cluster
```

The steps need to be printed on the CLI

Here are the install steps :
https://github.com/bcgov/cas-postgres/#steps-for-a-complete-fresh-install-will-lose-all-data