FailoverSupport defines an interface for different types of fail-over handlers, that provide different types of
behaviour for handling fail-overs during operations that can be interrupted by the fail-over process. For example,
the support could automatically retry once the fail-over process completes, could prevent an operation from being
started whilst fail-over is running, or could quietly abandon the operation or raise an exception, and so on.
TODO Continuation, extend some sort of re-usable Continuation interface, which might look very like this one.