The factory configuration file is directly included in Lightstreamer Server's distribution package, as the file may change slightly with the different versions of the Server.
If you use one of the Lightstreamer's official docker images, then the factory file is in the image at the /lightstreamer/conf/lightstreamer_conf.xml path and you can extract it with the "docker cp" command.
If you have built your docker image directly from Lightstreamer Server's distribution package, you can find it in the original package at the same path.