doc: Update track_io_timing documentation to mention pg_stat_io.

The I/O timing information collected when track_io_timing is
enabled is now documented to appear in the pg_stat_io view,
which was previously not mentioned.

This commit also enhances the description of track_io_timing
to clarify that it monitors not only block read and write
but also block extend and fsync operations. Additionally,
the description of track_wal_io_timing has been improved
to mention both WAL write and WAL fsync monitoring.

Backpatch to v16 where pg_stat_io was added.

Author: Hajime Matsunaga
Reviewed-by: Melanie Plageman, Nazir Bilal Yavuz, Fujii Masao
Discussion: https://postgr.es/m/TYWPR01MB10742EE4A6F34C33061429D38A4D52@TYWPR01MB10742.jpnprd01.prod.outlook.com

Author: MasaoFujii

doc/src/sgml/config.sgml

@@ -8319,7 +8319,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         measure the overhead of timing on your system.
         I/O timing information is
         displayed in <link linkend="monitoring-pg-stat-database-view">
-        <structname>pg_stat_database</structname></link>, in the output of
+        <structname>pg_stat_database</structname></link>,
+        <link linkend="monitoring-pg-stat-io-view">
+        <structname>pg_stat_io</structname></link>, in the output of
         <xref linkend="sql-explain"/> when the <literal>BUFFERS</literal> option
         is used, in the output of <xref linkend="sql-vacuum"/> when
         the <literal>VERBOSE</literal> option is used, by autovacuum

doc/src/sgml/monitoring.sgml

@@ -180,12 +180,12 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
 
   <para>
    The parameter <xref linkend="guc-track-io-timing"/> enables monitoring
-   of block read and write times.
+   of block read, write, extend, and fsync times.
   </para>
 
   <para>
    The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
-   of WAL write times.
+   of WAL write and fsync times.
   </para>
 
   <para>