chart: Upgrade postgres dependency to latest major version

[mkilchhofer]

Upgrade to latest postgresql dependency

Bitnami released a new major version of the postgresql dependency. As major chart upgrades are sometimes tricky, let's upgrade that dependency before additional majors arrive.

How to use

Nothing special.

Testing done

Pushed the helm chart to my own helm repository (chartmuseum) and upgraded my nebraska instance.

[joaquimrocha]

LGTM. Maybe @yolossn can also take a look.

[joaquimrocha]

And thanks a lot @mkilchhofer