Update max_convex_hulls description

[iche033]

🦟 Bug fix

Summary

Update <max_convex_hulls> description based on the recommendation in https://github.com/gazebosim/gz-physics/pull/606#pullrequestreview-1956282332.

This parameter now determines the max number of submeshes that will be in the final decomposed mesh.

Checklist

• [x] Signed all commits for DCO
• [x] 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.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.44%. Comparing base (836dd42) to head (ba3072f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1386 +/- ## ======================================= Coverage 92.44% 92.44% ======================================= Files 134 134 Lines 17812 17812 ======================================= Hits 16467 16467 Misses 1345 1345 ```

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