Right now the AsyncRequestsSender has a stopRetrying method that sets a boolean flag which prevents requests from retrying, but it does not cancel outstanding network requests. We should change it to use cancellation tokens, which would allow us to cancel in flight requests and return sooner. As part of this we should update this call to scheduleRemoteCommand to use the newer future-returning version of that API that takes a cancellation token.

I'm creating this ticket as a prerequisite for SERVER-50342 (create a generic async runCommand), since doing the "modernization" of the ARS and refactoring it into a reusable function seemed like too much to do in one go.