Create example of traefik on host network for obtaining ingress source IP's

The ingress routing mesh loses the client source IP, and some web apps need this. This enhancement would add an example/option for placing traefik on --network host so it can capture those source IP's and send them as host headers to backend services on an overlay network.

With traefik this makes the whole thing a bit more complex because we now must have a traefik replica on every node (global mode) which means we can't cheat with the TOML config file and cert files like we can with a single-replica traefik service. We'll need a config backend for traefik to make this work.

BretFisher / dogvscat

Create example of traefik on host network for obtaining ingress source IP's #9