Ability to get ownership of error of response

[ahmadbky]

The HttpResponse struct allows to get a reference to the optional error with its error() method, but we can't retrieve its ownership, which could be useful when mapping error reponses in middlewares.

It would be useful to have an additional method to get the ownership of the error.

[vinibuzzacaro]

When you say get ownership it makes me think of creating a into_error() method where the HttpResponse would be consumed to return the Option. But I think that's not exactly what you want. So maybe we should return a cloned Error struct?