Fixes for Jetson Nano build

[hmakelin]

Small fixes to make gisnav and mapserver services work on e.g. a Jetson Nano:

• Install GDAL separately for gisnav docker image: fixes potential error when installing geopandas later on (see e.g. https://stackoverflow.com/questions/62299567/error-installing-geopandas-a-gdal-api-version-must-be-specified-in-visual-st)
• Preload libgomp for gisnav docker image
• Add arm64 docker compose override for mapserver docker image
• Documentation updates