Further improve the postgresql upgrade message

Related to !1166 (merged)

On fresh installation the postinst message will be printed for postgresql update.

This has a potential to confuse new users as they just installed the latest available pacakge and they would expect the latest and greatest. We purposely did not change the default version of postgresql to avoid further confusing the users.

We should discuss whether it is better to just flat out not print the message on new installations or automatically upgrade fresh installations.

@gitlab-build-team thoughts?