Extract mbus configuration

Extract Mbus configuration logic into https://github.com/soomo/soomo-mbus-configuration.  This means that the core code in this repo will now focus on sending and receiving messages.  Whenever we want to update the ConfigBuilder with configuration changes, we can bump the version of the configuration gem without touching this one.  We can also deploy configuration changes, etc.  This gem will still depend on that gem for accessing the configuration, but it will have a stable API to do so, likely on `Mbus::Configuration` or `Mbus::Config` for short.