[DRAFT] Port Websocket server from gz-launch

[iche033]

Marked as draft to get CI working first

🎉 New feature

Related issue: gazebosim/gz-launch#288

Depends on these CI infra PRs:

• Homebrew: gz-sim10: depend on libwebsockets osrf/homebrew-simulation#2985
• Ubuntu: Add libwebsockets-dev dependency gazebo-release/gz-sim10-release#4
• Conda: Add libwebsockets dependency to conda gazebo-tooling/release-tools#1265

Summary

Port websocket_server plugin and the example gzweb visualization demo from gz-launch. Main changes are:

• converted the websocket server from a gz-launch plugin to a gz-sim system: i.e. gz-sim-websocket-server-system
  • updated to parse plugin params from SDF elements instead of using tinyxml
  • fixed various lint and compile warnings
• moved example gzweb demo files to examples/scripts/websocket_server
  • it includes a websocket_server.sdf world for testing
• Updated documentation in WebsocketServer.hh in the websocket_server system and README.md in the demo
• Added libwesockets as optional dependency

Test it

There is a simple websocket server demo world with a gzweb web page in examples/scripts/websocket_server. See README.md in that directory.

In summary, you can try these following steps:

1. Launch demo world with websocket server system

   cd examples/scripts/websocket_server
   gz sim -v 4 websocket_server.sdf -s
   

2. Connect gzweb to the websocket server for web visualization. This can be done by either

   1. Opening examples/scripts/websocket_server/index.html (materials not working, same issue in gz-launch), or
   2. Visiting https://app.gazebosim.org/visualization and hit Connect

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.