Determine if we should remove IPostCommitHandler

[jmzagorski]

If you have an IRequestHandler<T, R>, you can technically create a policy to run any handlers for R until you have no policy handlers or the subsequence handler is IRequestHandler<R, R>. This policy, by default, runs after the transaction anyway. You would have to take care that the Responses aggregated on top of each other so the response back to the user has all the data needed for an appropriate response.