update OpenStructure version to "latest" in Dockerfile

Changed the OpenStructure version from "2.3.0" to "latest" to ensure the use of an available version.

projects/docker/Dockerfile

-ARG VERSION_OST="2.3.0"
+ARG VERSION_OST="latest"
 FROM registry.scicore.unibas.ch/schwede/openstructure:${VERSION_OST}
 ## We need to declare ARGs again which were declared before the build stage
 ## (FROM directive), otherwise they won't be available in this stage.