pg_waldump: Add support for reading WAL from tar archives

pg_waldump: Add support for reading WAL from tar archives

pg_waldump can now accept the path to a tar archive (optionally
compressed with gzip, lz4, or zstd) containing WAL files and decode
them.  This was added primarily for pg_verifybackup, which previously
had to skip WAL parsing for tar-format backups.

The implementation uses the existing archive streamer infrastructure
with a hash table to track WAL segments read from the archive.  If WAL
files within the archive are not in sequential order, out-of-order
segments are written to a temporary directory (created via mkdtemp under
$TMPDIR or the archive's directory) and read back when needed.  An
atexit callback ensures the temporary directory is cleaned up.

The --follow option is not supported when reading from a tar archive.

Author: Amul Sul <sulamul@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Euler Taveira <euler@eulerto.com>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Zsolt Parragi <zsolt.parragi@percona.com>
discussion: https://postgr.es/m/CAAJ_b94bqdWN3h2J-PzzzQ2Npbwct5ZQHggn_QoYGhC2rn-=WQ@mail.gmail.com