Enhance Point2Grid to check "coordinates" variable attribute for ingesting non-traditional grids

Describe the Enhancement

In its current state, point2grid functions properly for MET NetCDF point observation files, via python embedding, GOES-16/17 input files in NetCDF format, or a CF-compliant netCDF file. However a user-provided netCDF file in tripolar projection from NOAA caused an error when running the point2grid tool as it is not in CF-compliant format and uses "TLAT" and "TLON" for a coordinate system.

As part of the ongoing effort to support tripolar projection, point2grid should be enhanced to check the "coordinates" attribute of the variable field being evaluated for typical tripolar projection coordinate systems (TLAT/TLON, ULAT/ULON, NLAT/NLON, ELAT/ELON) and if found, continue with the interpolation as requested.

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[ ] METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy

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dtcenter / MET