pgsql: Add contrib/pg_logicalinspect.

Add contrib/pg_logicalinspect.

This module provides SQL functions that allow to inspect logical
decoding components.

It currently allows to inspect the contents of serialized logical
snapshots of a running database cluster, which is useful for debugging
or educational purposes.

Author: Bertrand Drouvot
Reviewed-by: Amit Kapila, Shveta Malik, Peter Smith, Peter Eisentraut
Reviewed-by: David G. Johnston
Discussion: https://postgr.es/m/ZscuZ92uGh3wm4tW%40ip-10-97-1-34.eu-west-3.compute.internal

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7cdfeee320e72162b62dddddee638e713c2b8680

Modified Files
--------------
contrib/Makefile                                   |   1 +
contrib/meson.build                                |   1 +
contrib/pg_logicalinspect/.gitignore               |   6 +
contrib/pg_logicalinspect/Makefile                 |  31 ++++
.../pg_logicalinspect/expected/logical_inspect.out |  52 +++++++
contrib/pg_logicalinspect/logicalinspect.conf      |   1 +
contrib/pg_logicalinspect/meson.build              |  39 +++++
.../pg_logicalinspect/pg_logicalinspect--1.0.sql   |  43 ++++++
contrib/pg_logicalinspect/pg_logicalinspect.c      | 167 +++++++++++++++++++++
.../pg_logicalinspect/pg_logicalinspect.control    |   5 +
.../pg_logicalinspect/specs/logical_inspect.spec   |  34 +++++
doc/src/sgml/contrib.sgml                          |   1 +
doc/src/sgml/filelist.sgml                         |   1 +
doc/src/sgml/pglogicalinspect.sgml                 | 143 ++++++++++++++++++
src/backend/replication/logical/snapbuild.c        |  99 +++++++-----
src/backend/utils/adt/arrayfuncs.c                 |   6 +
src/include/replication/snapbuild.h                |   4 +
src/include/replication/snapbuild_internal.h       |   3 +
18 files changed, 598 insertions(+), 39 deletions(-)