add gdal-config wrapper

[jgrn307]

https://gdal.org/programs/gdal-config.html#gdal-config

[Jo-Schie]

I'd like to use the GDAL_CACHEMAX option to increase the default GDAL raster block cache size. At the moment the function allocates 500 MB which is very low in my opinion. For me one of the main advantages of GDAL over e.g. the internal raster package is speed. At the moment this is limited without this option. Any plans to implement this?

[Jo-Schie]

I think I figured out how the internals work and I was able to include this experimentally for gdal_rasterize see here.