Add GGM10, Mexican geoid model

Grid files for Mexican geoid model, from Mexico ITRF2008 to NAVD88 height

See related PR OSGeo/PROJ#2889

Generated with this script:

sed -i 's/^[0-9]/-&/' GGM10.txt  # longitude must be negative on western hemisphere

docker run --user $(id -u):$(id -g) --workdir $PWD \
             --rm -v /home:/home osgeo/gdal:alpine-normal-latest python3 ./PROJ-data/grid_tools/vertoffset_grid_to_gtiff.py \
             --type GEOGRAPHIC_TO_VERTICAL \
             --source-crs EPSG:6364 \
             --target-crs EPSG:5703 \
             --area-of-use "Mexico" \
             --copyright "Derived from work by INEGI. CC BY 4.0 https://creativecommons.org/licenses/by/4.0/" \
             GGM10.txt mx_inegi_ggm10.tif

OSGeo / PROJ-data

Add GGM10, Mexican geoid model #72