The interface for request middleware.

Pipes are analogous to the behaviour of Plug. Requests enter the Orbit.Endpoint and are passed through a series of pipes that sequentially process the request, and at the end of the pipeline the response is sent to the client.

A pipe may also be simple 2-arity anonymous function that implements the same typespec as call/2.

When you use Orbit.Router or use Orbit.Controller, the call/2 callback is injected into the module, turning it into a Pipe.