Add fluid-fluid case with periodically changing flow direction

[uekerman]

There are already nice tutorials with backwards flow, e.g. https://precice.org/tutorials-partitioned-backwards-facing-step.html
It would be nice to showcase also a scenario where the flow direction is changing periodically, which is a common situation in many bio-mechanical applications.

This could also simply be an extension of https://precice.org/tutorials-partitioned-pipe.html