BUG #16074: Consistently link latest repo RPM release to pgdg-redhat-repo-latest

The following bug has been logged on the website:

Bug reference:      16074
Logged by:          Matt Saladna
Email address:      msaladna@apisnetworks.com
PostgreSQL version: 11.0
Operating system:   RHEL 8
Description:

RHEL7 and prior repositories link the latest pgdg repo release to
pgdg-redhat-repo-latest.noarch.rpm. This is not the case with RHEL8:

RHEL7 with Postgres 11:
pgdg-redhat-repo-42.0-5.noarch.rpm    2019-Sep-27
13:28:13    5.8K    application/x-redhat-package-manager
pgdg-redhat-repo-latest.noarch.rpm    2019-Sep-27
13:28:13    5.8K    application/x-redhat-package-manager

And from RHEL8 with Postgres 11:
pgdg-redhat-repo-42.0-5.noarch.rpm    2019-Sep-27
13:25:39    9.9K    application/x-redhat-package-manager

-latest is properly linked in RHEL8/Postgres 12, but not with 11, 10, or
9.6.