pgsql: Add pg_ls_summariesdir().

Add pg_ls_summariesdir().

This function returns the name, size, and last modification time of
each regular file in pg_wal/summaries.  This allows administrators
to grant privileges to view the contents of this directory without
granting privileges on pg_ls_dir(), which allows listing the
contents of many other directories.  This commit also gives the
pg_monitor predefined role EXECUTE privileges on the new
pg_ls_summariesdir() function.

Bumps catversion.

Author: Yushi Ogiwara
Reviewed-by: Michael Paquier, Fujii Masao
Discussion: https://postgr.es/m/a0a3af15a9b9daa107739eb45aa9a9bc%40oss.nttdata.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4e1fad37872e49a711adad5d9870516e5c71a375

Modified Files
--------------
doc/src/sgml/func.sgml                       | 24 ++++++++++++++++++++++++
src/backend/catalog/system_functions.sql     |  4 ++++
src/backend/utils/adt/genfile.c              |  9 +++++++++
src/include/catalog/catversion.h             |  2 +-
src/include/catalog/pg_proc.dat              |  6 ++++++
src/test/regress/expected/misc_functions.out |  6 ++++++
src/test/regress/sql/misc_functions.sql      |  1 +
7 files changed, 51 insertions(+), 1 deletion(-)