postgis package logic is broken for EL8/EL9

Describe the Bug

This is a followup issue for #1521 / #1519. There's some logic in manifests/params.pp to figure out the correct name for the postgis package:

      if $postgresql::globals::postgis_package_name {
        $postgis_package_name = $postgresql::globals::postgis_package_name
      } elsif $facts['os']['release']['major'] == '5' {
        $postgis_package_name = 'postgis'
      } elsif $postgis_version and versioncmp($postgis_version, '2') < 0 {
        $postgis_package_name = "postgis${package_version}"
      } else {
        $postgis_package_name = "postgis2_${package_version}"
      }

There's no matching package on EL8/EL9 (tested via https://pkgs.org/search/?q=postgis). Also there seems to be no suitable acceptance test to verify this is actually working.

Expected Behavior

Aa working postgresql installation on EL8/EL9 with postgis extension

Steps to Reproduce

Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'

Environment

• Version [e.g. 1.27.0]
• Platform [e.g. Ubuntu 18.04]

Additional Context

Add any other context about the problem here.

Start in manifests/params.pp and compare the existing package-name branches with EL8/EL9 package availability. Add or update an acceptance test for a working PostgreSQL installation with the PostGIS extension on EL8/EL9, and use it to verify the package logic.