doc: Document effects of ownership change on privileges

doc: Document effects of ownership change on privileges

Explicitly document that privileges are transferred along with the
ownership. Backpatch to all supported versions since this behavior
has always been present.

Author: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: David G. Johnston <david.g.johnston@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Josef Šimánek <josef.simanek@gmail.com>
Reported-by: Gilles Parc <gparc@free.fr>
Discussion: https://postgr.es/m/2023185982.281851219.1646733038464.JavaMail.root@zimbra15-e2.priv.proxad.net
Backpatch-through: 14