* add docs for the retry-exchange

* Apply suggestions from code review
Co-Authored-By: Will Golledge <35961363+wgolledge@users.noreply.github.com>

* Put retryExchange options into a list, add a list of available exchanges to concepts/core

* move order of retryExchange in docs so that it sits between the cacheExchange and fetchExchange

* create new retryExchange api page

* Add introduction and rename file

* Add missing order key to retry API page

* Add missing link to API index page
Co-authored-by: Will Golledge <35961363+wgolledge@users.noreply.github.com>
Co-authored-by: wgolledge <wiggiumg@gmail.com>
Co-authored-by: Phil Pluckthun <phil@kitten.sh>