Remove ArtifactsWrappers and document artifacts

[Sbozzolo]

Following ClimaArtifacts

Artifacts downloaded

### to be moved to ClimaArtifacts
- [ ] cesm2_albedo
- [ ] bareground_albedo
- [ ] experiment_fluxnet_data (for each site)
- [ ] water_conservation_test_data (flux_dataset, dirichlet_dataset)
- [ ] richards_eqn_bonan_data (clay, sand)
- [ ] topmodel_data
- [ ] lehmann_assouline_or2008_evaporation_data
- [ ] huang_et_al2011_soil_van_genuchten_data
- [ ] mizoguchi1990_soil_freezing_data
- [ ] 2_str_test_data (only used in test)