Make `RetryPolicy` aware of request and response

[bonsairobo]

Motivations

Right now, RetryPolicy only knows how many times a request has failed, but it doesn't have any other context about the request+response in question. It would be nice to customize the retry policy based on the value of request and response.

Solution

Add some parameters to RetryPolicy::should_retry, at a minimum:

• url of the request
• StatusCode of the response

And then maybe there should be more, but I think these are the most important.

Alternatives

Writing my own retry middleware.