Add CMake upstream(3.20.0) version of FindPostgreSQL.cmake, to avoid
server-related headers lookup.
Avoid using the Qt version of the PostgreSQL module, if it's
older than the CMake's one.
Fixes: QTBUG-89639
Change-Id: I71a0c3508000901969933aea8a08d1ad431db711
Reviewed-by: Craig Scott <craig.scott@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
