This patch drops the kOS setup entirely, since it has been around for
months now, but seems to be impractical as I still didn't bother to put
it in production. Apparently the usage of Fedora Server with the
existing automatic update mechanisms has proven suffient for now.

This patch provides the first release of kOS, a new Fedora CoreOS remix,
that is focused on the current setup of the SI infrastructure.

It basically implements all the little hacks and adjustments that are
currently active on the (existing) Fedora Server nodes running the
infrastructure and will provide a better replacement as soon as they are
put in production.

This patch adds a new container image for synadm, which should help to
administrate synapse using a CLI.

Adding a new helm chart to deploy functional mail server on Kubernetes.
It's composed of postfix and dovecot so far and handles user management
using Kubernetes secrets.

This patch adds some external links to the docs navigation section.
Since mdbooks doesn't support this by default, this adds a JS file as
workaround, which avoids forking the theme or writing an extension for
mdbooks.

References:
https://github.com/rust-lang/mdBook/issues/1354