add soilgrids organic carbon density as artifact

[EvaMarieMetz]

I added a 1 degree resolution soil organic carbon density (ocd) artifact based on soil grids data.

The artifact is based on the existing soilgrids artifact. The only difference is, that an area weighted average is used to derive the 1x1 degree dataset from the 5km resolution data.

Checklist:

• I created a new folder soilgrids_ocd
  • I added a README.md in that that folder that
    • describes the data and processing done to it
    • lists the sources of the raw data
    • lists the required citation, licenses
  • If applicable (e.g., for Creative Commons), I added a LICENSE file
  • I added the scripts that retrieve, process, and produce the artifact
  • I added the environment used for such scripts (typically, Project.toml
    and Manifest.toml)
  • I added the OutputArtifacts.toml file containing the information
    needed for package developers to add $artifact_name to their package
• I uploaded the artifact folder to the Caltech cluster (in
  /resnick/groups/esm/ClimaArtifacts/artifacts/$artifact_name)
• I added the relevant code to the Overides.toml on the Caltech Cluster
  (in /resnick/groups/esm/ClimaArtifacts/artifacts/Overrides.toml)
• I added a link to the main README.md to point to the new artifact

[github-actions]

⚠️ Contributor License Agreement required

The following contributor(s) must sign the CLA before this PR can be merged:

• @EvaMarieMetz

Please visit https://ecodesign.clima.caltech.edu/cla/ to review and sign the CLA.

How to sign: Authenticate with GitHub then click the "I agree" button.

Once completed, re-run the checks on this PR.