Add example configuration for rsnapshot

[widhalmt]

The idea is to have rsnapshot configuration that will help with the most basic installation of tools we are supporting.

I'm still undecided if this is a thing to provide as a copy&paste documentation for variables or add a separate feature you can en- or disable via boolean variable.

What I'm thinking of are things like a very easy way to tell the role: "Host is an Icinga 2 server" and you get automatic backups of Icinga configuration, Icinga CA, Icinga statefiles etc. whatever we see as backup worthy in an installation.

This is issue has a focus on providing the basics for further development:

• Decide whether there should be copy&paste examples or configurable "features" to activate
• Build code for what is neccessary to build the first backup of a tool
• Use Icinga 2 servers including CA as an example for a first setup
• Keep in mind that there are a lot of different tools to support, but keep their implementation for other issues. You may well open up new issues for Elastic Stack, Graylog, Puppet, etc. that build upon your solution