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.