[WIP] STI foreman provider

This creates the models to be used for creating the foreman configuration provider.



This feels like it needs a lot more.
Did I miss anything?
/cc @gmcculloug @brandondunne 
We are passing this to foreman, which requests a string, I do not know if they can handle a `URI`. It is fragile and even fails if there is a trailing slash.

Most rest clients (foreman api is using `RestClient::Resource.new`) document the first parameter as a string.

It would probably be easier if we could just ask the user to enter the base url "http://host:port" instead of asking for 3 separate fields fields: `host`, `port`, `ssl?`.

I'll start playing with their api and see if it is easy to pass in a URI.