Fixes issue #2903 (backport #2907)

[mergify]

🦟 Bug fix

Fixes #2903

Summary

This PR fixes issue #2903 and prevents the server from segfaulting if the plugin fails to load correctly. It prints an error that the plugin was misconfigured and continues executing ahead.

At some point we should revisit our plugin loading interface. A lot of work is placed in the developers hands to understand internals of gazebo's lifecycle. For starters, we should try to call Configure after the entities are created. It'd also be nice to be able to return an error during Configure and just not care about executing the plugin in the future. I'll open a ticket outlining how we can go about doing this with minimal interruptions to out currently existing codebase.

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 #2907 done by [Mergify](https://mergify.com).