Installing extension inside a Dockerfile

dear Andras, my question is how to Slicer’s extension manager to install the extension. Cause docker container is non-GUI. Please help me. Thanks a lot .
Btw, my question is report here. https://discourse.slicer.org/t/how-to-install-slicerrt-extension-in-docker-slicerdocker-container/21270?u=rosenty