Extract out providers to a new package

[engram-design]

Create a new package that’s a PHP abstraction library for provides (one that we’ll write). Similar to league/oauth or omnipay as something any PHP package can use, not just for Craft.

This will help support different rate fetching and better abstraction for labels and tracking along with simplifying Postie itself.

From research there’s nothing out there at the moment that isn’t a paid service.

[engram-design]

Updated in 4.0.0 and hello verbb/shippy