Update links in point cloud to mesh tutorial and fix screenshot link

[iche033]

🦟 Bug fix

Related: gazebosim/gazebo_test_cases#1264

Summary

Update links to point to gz-sim9 branch and fix one screenshot link

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.76%. Comparing base (712643f) to head (944d7db).
Report is 9 commits behind head on gz-sim9.

Additional details and impacted files

@@             Coverage Diff             @@
##           gz-sim9    #2632      +/-   ##
===========================================
- Coverage    68.80%   68.76%   -0.04%     
===========================================
  Files          341      341              
  Lines        33037    33049      +12     
===========================================
- Hits         22730    22727       -3     
- Misses       10307    10322      +15     

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