Giving a `nil` for `MyApp.Repo` configuration's `:pool` creates error

I also prefer to only use runtime.exs as much as possible, except for when it’s not possible.

I have proof of concept for a unrelated thing, but in the the docs you can read how I use runtime.exs:

https://github.com/Exadra37/elixir-phoenix-360-web-apps/blob/dev_runtime-wip/TRY_IT_OUT.md