Add an OpenFOAM debugging option for multiple time step runs

[nwagenbrenner]

We reuse the OpenFOAM case directory for simulations with multiple time steps to avoid re-building the mesh and other costly operations.The case reuse can make debugging difficult and prevents users from being able to work with the full 3D output from timesteps other than the final time step. We should add an option in CMake to save intermediate case files.