Regroup tutorials into four categories

[mabelzhang]

🎉 New feature

Plenty of room for feedback on the groupings

Summary

Regroup tutorials into the 4 categories (tutorials, how-to guides, explanation, reference) recommended by the best-practice guide for documentation here https://documentation.divio.com/ which is followed by the ROS 2 documentation, as mentioned in this comment: #2028 (review)

(Also fix a few formatting problems I saw here and there)

Test it

Preview the rendered Doxygen pages in build/gz-sim8/doxygen/html/tutorials.html

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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 ✅

Comparison is base (451dcf3) 65.66% compared to head (59b777f) 65.66%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2109   +/-   ##
=======================================
  Coverage   65.66%   65.66%           
=======================================
  Files         324      324           
  Lines       30938    30938           
=======================================
+ Hits        20314    20315    +1     
+ Misses      10624    10623    -1     

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[mabelzhang]

Ready for review

[mabelzhang]

@azeey Do you want to take a look at this PR or is the green check good?

[azeey]

LGTM!