Add websocket server tutorial

[iche033]

🎉 New feature

Depends on #2792

Summary

Add tutorial for websocket server system. It shows a couple of simple examples of launching the websocket server, both from SDF world and from cmd line. The tutorial also includes a migration guide on how to port the websocket server .gzlaunch plugin files to to gz-sim.

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.