Feat install_db.sh: add Postgis 3 postgis_raster extension
Feat install_db.sh: add Postgis 3 postgis_raster extension

Check installed Postgis version, if version is greather or equal to 3.0,
we install "postgis_raster" extension.

Closes #946

PnEcrins/GeoNature,PnEcrins/GeoNature,PnEcrins/GeoNature,PnEcrins/GeoNature