[WIP] Create an example Scaffolding::CompletelyConcrete::SimpleSingleton resource

[ps-ruby]

https://github.com/bullet-train-co/bullet_train/issues/532

[jagthedrummer]

@andrewculver Is this something you want to merge? It's not entirely clear to me what you're asking for in #532. I'm not sure if you're wanting to just see an example branch that you can point people to, or if it's something that should fully live in the starter repo.