Fire create_upper_paths_hook for UPPERREL_PARTIAL_GROUP_AGG

Greetings

create_partial_grouping_paths() builds the UPPERREL_PARTIAL_GROUP_AGG
upper relation.  It already calls the FDW callback GetForeignUpperPaths
there, but never calls create_upper_paths_hook, the general-purpose
hook that non-FDW extensions use to add paths. UPPERREL_PARTIAL_DISTINCT
doesn't have this gap: create_partial_distinct_paths() calls both
GetForeignUpperPaths and create_upper_paths_hook for it.

This patch adds the missing create_upper_paths_hook call right next to
the existing GetForeignUpperPaths call, so a non-FDW extension can add
partial aggregation paths at the same point an FDW already can, before
those paths are gathered and a Finalize Aggregate is built on top.

It's a small, self-contained planner change with no effect on existing
plans unless an extension registers create_upper_paths_hook and adds
paths at this new call site.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com