As mentioned above, the websocket is in gz-launch. You can run the websocket from the command line using ign launch (as opposed to ign gazebo), like so:
ign launch gz-launch/examples/websocket.gzlaunch
(That’s this file gz-launch/websocket.gzlaunch at gz-launch6 · gazebosim/gz-launch · GitHub)
It’s basically the same setup as the SubT .ign file linked above, but this one is shipped with Gazebo.