Fixes #1636. Add History regrid_method attribute

[mathomp4]

Description

This PR adds a new variable metadata to history corresponding to the regrid method used. Testing shows it to be zero-diff and all seems to work.

Also, this fixes a bug where in NEAREST_STOD was not supported by mistake.

Related Issue

Closes #1636

Motivation and Context

We could eventually have different regridding methods per variable. Now we at least have per-collection. By adding some extra metadata, we can at least tell how each variable was regridded:

        float BCDP001(time, lat, lon) ;
                BCDP001:_FillValue = 1.e+15f ;
                BCDP001:add_offset = 0.f ;
                BCDP001:fmissing_value = 1.e+15f ;
                BCDP001:long_name = "Carbonaceous Aerosol Dry Deposition (Bin %d)" ;
                BCDP001:missing_value = 1.e+15f ;
                BCDP001:regrid_method = "conserve_2nd" ;
                BCDP001:scale_factor = 1.f ;
                BCDP001:standard_name = "Carbonaceous Aerosol Dry Deposition (Bin %d)" ;
                BCDP001:units = "kg m-2 s-1" ;
                BCDP001:valid_range = -1.e+15f, 1.e+15f ;
                BCDP001:vmax = 1.e+15f ;
                BCDP001:vmin = -1.e+15f ;

How Has This Been Tested?

Ran GEOS and it built and ran and was zero-diff

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog

[mathomp4]

Just realized. I need to test this without GEOS-ESM/GEOSgcm_App#344 as they might come in at different times. I mean...it should work, but let's be careful!

[mathomp4]

Just realized. I need to test this without GEOS-ESM/GEOSgcm_App#344 as they might come in at different times. I mean...it should work, but let's be careful!

I have done this and all seems to work and I get regrid_method. So...I'll undraft!