Add aux_clm test that generates history_fields_fates.rst

[samsrabin]

The clm/extra_outputs testmod makes it so that either history_fields_nofates.rst or history_fields_fates.rst is generated, depending on whether it's a FATES compset. There is one test in aux_clm doing this with a non-FATES compset, but none with FATES. This means that if we want to update the history fields files in the docs, we have to manually run a FATES compset.

I think the easiest thing to do would be to just add --clm/extra_outputs to the testmods tag of an existing FATES test.