WithFullJitter?

[craigpastro]

Hello! I realize I could add this middleware myself, but I was wondering if you would be interested in adding a WithFullJitter middleware? Full jitter would return a duration between 0 and Next(). According to https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/, full jitter is better than equal jitter (which is essentially what WithJitter and WithJitterPercentage are).

If you think it is a good idea I am happy to create a PR.