Expose timeout field in Request

[TAYTS]

I want to retrieve the timeout with custom RoundTripper without creating another wrapper for the Request to tweak how the timeout is being handled or is it possible we could support user custom values similar to RequestCtx.userValues to allow the flexibility to inject value to the request?
The use case for this is that the current HostClient timeout is set for the whole request and for stream response I would like to fail the request if the response header is slow but wait for the response body for slightly longer time or a constant deadline extend if there are incoming data from stream

[erikdubbelboer]

I would be open to a pull request to add a method to expose this. But it needs some good documentation to make clear what it's for.