Update launch tutorial

[iche033]

🦟 Bug fix

Related issue: gazebosim/gazebo_test_cases#1971 (comment)

Summary

• Updated instructions in the tutorial
• Fixed joint state publisher system name in factory.gzlaunch
• Updated simFactory plugin to return true after successfully loading the plugin

Checklist

• Signed all commits for DCO
• Added tests
• 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)
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