Add Polish geoid model PL-geoid2021

[AlexBass05]

EPSG v10.091 added the missing transformation for the latest Polish geoid model PL-geoid2021:

• https://epsg.org/transformation_10347/ETRF2000-PL-to-EVRF2007-PL-height-2.html
• https://epsg.org/transformation_10348/ETRF2000-PL-to-ETRF2000-PL-EVRF2007-PL-height-2.html

This unblocks the addition of that geoid model to PROJ.

License and source file: http://www.gugik.gov.pl/bip/prawo/modele-danych

This PR depends on OSGeo/PROJ#3812.

Related PR in PROJ: OSGeo/PROJ#3817

[rouault]

@AlexBass05
can you modify (and re-run) the build script to include a gdalwarp stage like the one used for pl_gugik_geoid2011-PL-EVRF2007-NH.tif, so that the raster produced is "north-up", which is a more usual practice

[AlexBass05]

@AlexBass05 can you modify (and re-run) the build script to include a gdalwarp stage like the one used for pl_gugik_geoid2011-PL-EVRF2007-NH.tif, so that the raster produced is "north-up", which is a more usual practice

@rouault
Thanks for pointing this out. Done. The respective warning issued by check_gtiff_grid.py is gone now.
I regenerated the index again.