Update model output schema with geospatial_lat/lon_min/max

[joshuatorrance]

I would like to add the following attributes to the model data output schema:

• geospatial_lat_min
• geospatial_lat_max
• geospatial_lat_units
• geospatial_lon_min
• geospatial_lon_max
• geospatial_lon_units

These are ACDD suggested attributes and will allow tools like intake to interact geospatially with the data, e.g. show region for dataset on a map, filter datasets based on geographic extent.

A couple of extra thoughts and info in this issue:.