BUG #17682: Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8))

The following bug has been logged on the website:

Bug reference:      17682
Logged by:          Eugen Konkov
Email address:      kes-kes@yandex.ru
PostgreSQL version: 15.1
Operating system:   Ubuntu
Description:

Hello, Team.

This documentation page should be updated:
https://www.postgresql.org/download/linux/ubuntu/

In addition to:
```
# Create the file repository configuration:
sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release
-cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

# Import the repository signing key:
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo
apt-key add -
```

Would be nice to mention: 
```
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | gpg
--dearmor | sudo tee /etc/apt/trusted.gpg.d/postgres.gpg
```