Fix image sizes in apply_force_torque tutorial

[azeey]

🦟 Bug fix

Fixes gazebosim/gazebo_test_cases#750

Summary

Uses the doxygen tag \image to avoid github URLs and specifies a percent width to fix the issues mentioned in gazebosim/gazebo_test_cases#750

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

Merging #2169 (5c778e8) into gz-sim7 (e007fa2) will not change coverage.
The diff coverage is n/a.

❗ Current head 5c778e8 differs from pull request most recent head 7a2fae7. Consider uploading reports for the commit 7a2fae7 to get more accurate results

@@           Coverage Diff            @@
##           gz-sim7    #2169   +/-   ##
========================================
  Coverage    65.02%   65.02%           
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  Files          356      356           
  Lines        28932    28932           
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  Hits         18814    18814           
  Misses       10118    10118