Updates to MHD BC functions for compatibility with new stores/packages

[joe-pitt]

Three changes (maybe should have separated these...):

1. Add optional "fp_species" that allows the footprint species to be specified in you have short lifetime and/or co2 footprints in the same object store as the inert footprints. The wind direction should be the same in all fps, but we need to specify an fp species in this case.
2. In the new object stores, wind_direction has become wind_from_direction
3. In recent versions of xarray we need to use .compute() in conjunction with .where(). See discussion here: Indexing with a boolean dask array is not allowed... hainegroup/oceanspy#332

[brendan-m-murphy]

This looks good, although it should be fixed on the OpenGHG side!