Document firewall and fail2ban host integration

[jonasbardino]

In native migrid deployments we rely on certain firewall rules for port forwarding, protecting against service overload and limiting e.g. password cracking attempts.
In the docker-migrid setup one needs to handle most such configuration on the host running the containers. Yet, there are some log files and configuration files generated in the actual build/deployment in play.
We need to at least document which components are in play and how a minimal such firewall and fail2ban setup can help fortify the site against abuse.

Added to milestone 1 because that is our own migration target, but in practice it really fits any production deployment.

[jonasbardino]

We have the firewall and fail2ban plays in our local ansible deployment of docker-migrid on the first such production and test sites. Please ask for the details if you want to help integrate or just use them somewhere else.