chart: disable collecting database size metric

[paulfantom]

What this PR does / why we need it

Disabling collecting database size statistics as this can be expensive and some of this data is also provided via node_exporter.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #652

Special notes for your reviewer

Checklist

• [x] Chart Version bumped
• [x] CLA signed

[onprem]

The postgres_exporter seems to be backing off, maybe we are using an older image for the exporter Back-off restarting failed container.

Update: nope, we are on the latest stable version.

[paulfantom]

I amended commit with an alternative approach to disabling this collector.