feat: abstract out more "providers"

[brent-hoover]

Do similar to what EspressoTS is doing here: https://doc.expresso-ts.com/docs/overview/providers where we de-couple the specific implementation of things usage. I think email providers will be a good place to try this out on

You should also be able to easily create your own type of provider type, say payment or fulfillment providers through a plugin, that then other plugins could fulfill. Again similar to how RC used to have a "payment" plug, that would then have various payment provider implementations.