pgsql: Add SQL functions to monitor the directory contents of replicati

Add SQL functions to monitor the directory contents of replication slots

This commit adds a set of functions able to look at the contents of
various paths related to replication slots:
- pg_ls_logicalsnapdir, for pg_logical/snapshots/
- pg_ls_logicalmapdir, for pg_logical/mappings/
- pg_ls_replslotdir, for pg_replslot/<slot_name>/

These are intended to be used by monitoring tools. Unlike pg_ls_dir(),
execution permission can be granted to non-superusers. Roles members of
pg_monitor gain have access to those functions.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Justin Pryzby
Discussion: https://postgr.es/m/CALj2ACWsfizZjMN6bzzdxOk1ADQQeSw8HhEjhmVXn_Pu+7VzLw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1922d7c6e1a74178bd2f1d5aa5a6ab921b3fcd34

Modified Files
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contrib/test_decoding/expected/slot.out | 21 ++++++++
contrib/test_decoding/sql/slot.sql | 6 +++
doc/src/sgml/func.sgml | 73 ++++++++++++++++++++++++++++
src/backend/catalog/system_functions.sql | 12 +++++
src/backend/utils/adt/genfile.c | 44 +++++++++++++++++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 22 +++++++++
src/test/regress/expected/misc_functions.out | 50 +++++++++++++++++++
src/test/regress/sql/misc_functions.sql | 21 ++++++++
9 files changed, 250 insertions(+), 1 deletion(-)