pgsql: Create functions pg_set_relation_stats, pg_clear_relation_stats.

Create functions pg_set_relation_stats, pg_clear_relation_stats.

These functions are used to tweak statistics on any relation, provided
that the user has MAINTAIN privilege on the relation, or is the database
owner.

Bump catalog version.

Author: Corey Huinker
Discussion: https://postgr.es/m/CADkLM=eErgzn7ECDpwFcptJKOk9SxZEk5Pot4d94eVTZsvj3gw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e839c8ecc9352b7754e74f19ace013c0c0d18613

Modified Files
--------------
doc/src/sgml/func.sgml | 94 +++++++++++++
src/backend/catalog/system_functions.sql | 10 ++
src/backend/statistics/Makefile | 4 +-
src/backend/statistics/meson.build | 2 +
src/backend/statistics/relation_stats.c | 210 +++++++++++++++++++++++++++++
src/backend/statistics/stat_utils.c | 94 +++++++++++++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 15 +++
src/include/statistics/stat_utils.h | 29 ++++
src/test/regress/expected/stats_import.out | 143 ++++++++++++++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/stats_import.sql | 98 ++++++++++++++
12 files changed, 700 insertions(+), 3 deletions(-)