By introducting a new command, the pass through proxy gets an execution
path. To allow for manual testing, but also for, probably more
important; getting started with integrating into the GitLab
architecture.

For logging we default to logrus, but these aren't structured yet. Which
should be improved later.

Config is added too, by parsing a TOML file. The path to this file is
passed as first argument to the praefect binary.