Response chain

[thomas-zahner]

The Client currently has a plugin_request_chain but no plugin_response_chain. It might make sense to add a response chain.

In the following snippet we can see how the request chain is traversed and we get the status. handle_github is the perfect candidate for an element in the internal default response chain.

let status = ClientRequestChains::new(vec![&self.plugin_request_chain, default_chain])
    .traverse(request)
    .await;

self.handle_github(status, uri).await

The question is how we define the ResponseChain type. Do we want to include the response body? This way plugin users could handle complicated use cases based on the response body.

pub type ResponseChain = Chain<Status, Status>;

or

pub type ResponseChain = Chain<(Body, Status), Status>;