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

doc/src/sgml/func.sgml

@@ -30530,6 +30530,30 @@ SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_ls_summariesdir</primary>
+        </indexterm>
+        <function>pg_ls_summariesdir</function> ()
+        <returnvalue>setof record</returnvalue>
+        ( <parameter>name</parameter> <type>text</type>,
+        <parameter>size</parameter> <type>bigint</type>,
+        <parameter>modification</parameter> <type>timestamp with time zone</type> )
+       </para>
+       <para>
+        Returns the name, size, and last modification time (mtime) of each
+        ordinary file in the server's WAL summaries directory
+        (<filename>pg_wal/summaries</filename>).  Filenames beginning
+        with a dot, directories, and other special files are excluded.
+       </para>
+       <para>
+        This function is restricted to superusers and members of
+        the <literal>pg_monitor</literal> role by default, but other users can
+        be granted EXECUTE to run the function.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>