do not add order by primary key if there are group by in the query

[pxpm]

WHY

BEFORE - What was wrong? What was happening before this PR?

Reported in Laravel-Backpack/community-forum#1107

In some rdms with sql_mode=only_full_group_by enabled, adding the primary key order resulted in an error, as the id column was not part of the group by clause.

In that regard, id never makes sense as part of a group by clause, as it should always be unique anyway.

AFTER - What is happening after this PR?

If there is a group by in the query we don't apply the default order by id.