Updates to the PostgreSQL 18 Beta 1 draft

Updates to the PostgreSQL 18 Beta 1 draft

Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Bruce Momjian <bruce@momjian.us>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Reviewed-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>