Add FFmpeg to the docker container

[SMEAC]

Would be good to see a FFmpeg installation added to the docker yaml so that isaac lab commands such as those mentioned here:
https://isaac-sim.github.io/IsaacLab/main/source/how-to/record_video.html can be usable. In the Docker Container without sudo, it is otherwise not so easy to install it, after the launchable is run.