Fix websocket proto request handling (backport #281)

[mergify]

🦟 Bug fix

Depends on gazebosim/gz-msgs#470

Fixes #246

Summary

Added workaround to fix websocket proto message request. Duplicate message types should be removed in gazebosim/gz-msgs#470. In addition, nested messages also leads to duplicate messages so worked around it by leaving it out of the response.

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)
• 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.

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This is an automatic backport of pull request #281 done by [Mergify](https://mergify.com).

[arilow]

Thanks @azeey!!