nest request_params within response params

[geemus]

We have recently had a number of asks to include more and more request params into the response to facilitate logging, error handling, etc. Although we did this on a one-off way at the top level of the response, this is getting a bit messy in terms of mixing request/response params and also leaves us in a position of having to do this again any time request changes.

Instead, we should consider nesting all of the request_params as a subkey within response. This keeps the request/response parts separate and should allow this to be more future-proof. We could then update the reader methods to point to this nested value. That being said, we may need or want to double write to the old values in the hash for backwards compatibility.

Overall we should discuss more and make sure the plan is clear before proceeding, but I wanted to capture this here for now as a place to have that discussion. See also initial discussion in #809