Prepare minimal set of required artifacts

[Sbozzolo]

As ClimaAtmos grows in complexity, more and more input files have started being required. At the moment, some of these files are pretty big (e.g., the aerosol file is multiple GBs). It is no longer feasable to automatically download them.

ClimaAtmos should maintain a minimal set of artifacts that can be automatically downloaded and that can be used for testing/exploration purposes.

In essence, this means reducing the spatial and temporal resolution of the files to the minimum possible.