Update physics_plugins tutorial

[shameekganguly]

🦟 Bug fix

Summary

• Removed redundant description of Gz Physics library which is already covered in the Introduction tutorial.
• Added references to Bullet and Bullet Featherstone plugins
• Replaced comparative list of features supported by different plugins with API and code links since this is easier to maintain going forward.

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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