Implement custom backends that an haproxy driver delegates the creation, updating, and deletion of haproxy instances.

A backend is described as the method and location in which resources and an instance or instances of haproxy are provisioned. This will make it easier to create many different backends that will use the same logic that will remain in the haproxy driver. The current implementation requires many different haproxy drivers to be created in which all drivers may have to reimplement the same code. This will also mean that multiple drivers can use the same backend without having to reimplement that backend in each driver, such as a synchronous driver and an asynchronous driver.