Feature: show Postgresql version in UI table

Please, answer some short questions which should help us to understand your problem / question better?

• Which image of the operator are you using? no idea
• Where do you run it - cloud or metal? Kubernetes or OpenShift? Cloud, Kubernetes (Zalando's installation)
• Are you running Postgres Operator in production? yes
• Type of issue? feature request

One instance of the postgres-operator can manage many PG-clusters, each of which has its own configuration.
The operator has an UI which shows a nice overview in table form.

In order to see which DBs still need to be upgraded, it would be nice if this table would have a column for the postgresql version running in each cluster (or which is configured, if that's easier and there are discrepancies).

Here is a mockup (built with Chrome developer tools editing a real running system):

Locate the operator UI's cluster overview table and trace the data source that supplies each cluster's configuration or status. Add a PostgreSQL version column using the available running or configured version, then verify that the table displays the version for each managed cluster.