Modern Debian-derived distributions will issue a deprecation warning for
the usage of apt-key add as listed here. Additionally, by using that
apt-key command, the given key is recognized as valid for all
repositories in /etc/apt/sources.list* -- not just this one.
By using the more modern mechanism, we can avoid that warning and also
import this key in such a way that it is only valid for this repository.
Other projects are also using this method; for instance:
https://apt.syncthing.net/
This post explains the security risks of apt-key:
https://blog.cloudflare.com/dont-use-apt-key/
