Add v4l2loopback configuration to streaming layer

layers/streaming.nix

-{ pkgs, ... }:
+{ pkgs, config, ... }:
 {
   imports = [
     ./desktop.nix
   ];
 
+  boot.extraModulePackages = with config.boot.kernelPackages; [ v4l2loopback ];
+  # modprobe v4l2loopback video_nr=42 card_label="IP Webcam"
+  # ffmpeg -i http://10.0.2.5:8080/video -vf format=yuv420p -f v4l2 /dev/video1
+
   environment.systemPackages = with pkgs; [
     obs-studio
     obs-wlrobs