Repository key handling changed

Hi,

previously, when installing postgresql-common from apt.postgresql.org,
it would pull in the pgdg-keyring package that contains the key for
the repository:

/usr/share/postgresql-common/pgdg/apt.postgresql.org.asc
/usr/share/postgresql-common/pgdg/apt.postgresql.org.gpg
/etc/apt/trusted.gpg.d/apt.postgresql.org.gpg -> /usr/share/postgresql-common/pgdg/apt.postgresql.org.gpg

In postgresql-common 246, this has been changed such that
postgresql-common itself contains the key files, and the trusted.gpg.d
symlink is created when a /etc/apt/sources.list.d/pgdg.list is found.

On upgrade, pgdg-keyring will be removed, but since the same set of
files is provided, nothing should change.

One caveat is that pgdg-keyring has /etc/apt/trusted.gpg.d/apt.postgresql.org.gpg
marked as conffile, so if the package is purged after the removal, the .gpg file
will be removed. (Workaround: reinstall postgresql-common, or don't
purge pgdg-keyring, or use an explicit key file (see below))

Additionally the apt.postgresql.org.sh installer script [1] has been
updated to write /etc/apt/sources.list.d/pgdg.sources in the modern
deb-822 style. By default it looks like this:

$ cat /etc/apt/sources.list.d/pgdg.sources
Types: deb
URIs: https://apt.postgresql.org/pub/repos/apt
Suites: bullseye-pgdg
Components: main
Signed-By: /usr/share/postgresql-common/pgdg/apt.postgresql.org.gpg

[1] https://salsa.debian.org/postgresql/postgresql-common/-/raw/master/pgdg/apt.postgresql.org.sh

The advantage is that the key for the repository is explicitly
specified, and the URI scheme has been upgraded to https://.
(Make sure systems have ca-certificates installed!)

I have not yet upgraded the installation instructions on
https://wiki.postgresql.org/wiki/Apt yet, since they are compatible
with either version of the key/scripts, but will do so over the next
days.

If you have questions, follow up here or ask on #postgresql-apt on
libera.

Christoph