Wrap built-in enums and add deprecation warning for unwrapped enums

[bdewater]

Addresses #468 - cc @kirs following our discussion at Rails World.

[bdewater]

I think before this gets merged, we should add a concrete example of using the wrapper, otherwise the original question I had #468 still goes unanswered and it looks like busy work. ThrottleEnumerator looks like a good one to use, but I don't remember if Kir told me Shopify uses it this way?

One other thing we could do but it's a less explicit API than generally seems to be the style used: we could detect if wrapping is needed when build_enumerator is called:

enumerator = build_enumerator(*arguments, cursor: cursor_position)
unless enumerator.is_a?(JobIteration.enumerator_builder::Wrapper)
  enumerator = enumerator_builder.wrap(enumerator)
end

[bdewater]

@Mangara addressed feedback and added an example, PTAL :)