Expose redirect url history to response

[unusual-thoughts]

Second attempt at #2606, now that the redirect mechanics use tower-http

Needs tower-rs/tower-http#583

This is an intermediate step towards implementing a full python requests-style history

While keeping every intermediate response might be costly, at least knowing if redirects happen and how many is useful to the user, and since we already store the info, why not make it available ?

This exposes the urls field from TowerRedirectPolicy to the Response, and adds a utility function to get a list of all the traversed urls, including the final one.

Closes #2314