it is possilbe to install plugins without opening GroIMP by using the following commands:

#install
java -jar core.jar --headless -- -cmd /pluginmanager/commands/installCMD=de.grogra.gltf;de.grogra.cli

#uninstall
java -jar core.jar --headless -- -cmd /pluginmanager/commands/uninstallCMD=de.grogra.gltf;de.grogra.cli

#disable
java -jar core.jar --headless -- -cmd /pluginmanager/commands/disableCMD=de.grogra.gltf;de.grogra.cli