UGRID / SGRID support

[sol1105]

Following up yesterday's brief discussion regarding UGRID / SGRID support, here are a few links:

• UGRID conventions: https://ugrid-conventions.github.io/ugrid-conventions/
• UGRID in CF: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.11/cf-conventions.html#ugrid-conventions
• UGRID cc-plugin: https://github.com/ioos/cc-plugin-ugrid
• xarray UGRID extensions:
  • uxarray: https://uxarray.readthedocs.io/en/latest/
  • xugrid: https://deltares.github.io/xugrid/
• SGRID conventions: https://sgrid.github.io/sgrid/
• SGRID cc-plugin: https://github.com/ioos/cc-plugin-sgrid

There are actually already cc-plugins for the verification of SGRID and UGRID conventions in development (even under the IOOS organization), so we probably should make use of those and contribute if needed.