Add Slovenian geoid model SLO-VRP2016/Koper

[AlexBass05]

This PR adds a new entry into the grid_alternatives-table to link to the GeoTIFF file for the Slovenian geoid model SLO-VRP2016/Koper added in PROJ-data: OSGeo/PROJ-data#93

See that there is already another EPSG-database update in preparation (#3609) but I don't expect any conflicts with this PR.

Example on master:

$ echo 46.0 14.5 0 | PROJ_DEBUG=2 cs2cs EPSG:4883  EPSG:4756+8690
pj_open_lib(proj.db): call fopen(.../install/share/proj//proj.db) - succeeded
pj_open_lib(proj.ini): call fopen(.../install/share/proj//proj.ini) - succeeded
Attempt at accessing remote resource not authorized. Either set PROJ_NETWORK=ON or proj_context_set_enable_network(ctx, TRUE)
pj_open_lib(https://isgeoid.polimi.it/Geoid/Europe/Slovenia/public/Slovenia_2016_SLO_VRP2016_Koper_hybrQ_20221122.isg): call fopen(https://isgeoid.polimi.it/Geoid/Europe/Slovenia/public/Slovenia_2016_SLO_VRP2016_Koper_hybrQ_20221122.isg) - failed
...
46.00	14.50 0.00

Example on this branch:

$ echo 46.0 14.5 0 | PROJ_DEBUG=2 cs2cs EPSG:4883  EPSG:4756+8690
pj_open_lib(proj.db): call fopen(.../install/share/proj/proj.db) - succeeded
pj_open_lib(proj.ini): call fopen(/.../install/share/proj/proj.ini) - succeeded
pj_open_lib(si_gurs_SLO-VRP2016-Koper.tif): call fopen(.../install/share/proj/si_gurs_SLO-VRP2016-Koper.tif) - succeeded
pj_open_lib(si_gurs_SLO-VRP2016-Koper.tif): call fopen(.../install/share/proj/si_gurs_SLO-VRP2016-Koper.tif) - succeeded
Using coordinate operation Slovenia 1996 to SVS2010 height (1) + Inverse of Ballpark geographic offset from VN-2000 to Slovenia 1996
pj_open_lib(si_gurs_SLO-VRP2016-Koper.tif): call fopen(.../install/share/proj/si_gurs_SLO-VRP2016-Koper.tif) - succeeded
46.00	14.50 -46.45