Expand FATES land use spin up testing to exercise AD spinup with `use_fates_potentialveg`

> While AD will likely be used for spin-up the main goal of the test is to exercise this `use_fates_potentialveg` to transient fates `use_fates_luh` mode. Per discussion with @ekluzek it would be good to include a test that exercises going from AD to `use_fates_potentialveg` spin up.