Backport GridConfig improvements to Citadel's Grid3D

[chapulina]

🎉 New feature

Part of gazebosim/gz-sim#1254

Summary

#324 made multiple improvements to GridConfig and Grid3D, and also consolidated them into the same plugin. That went into Fortress.

On Citadel, GridConfig is on ign-gazebo, while Grid3D is on ign-gui (GridConfig was moved to ign-gui in #236 ). So what this PR does is copy the GridConfig code from ign-gui6 into ign-gui3's Grid3D.

Test it

Load the Grid3D plugin from the menu on ign-gazebo, for example.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• 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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[codecov]

Codecov Report

Merging #363 (ce4a9a4) into ign-gui3 (a6afb94) will decrease coverage by 1.83%.
The diff coverage is 6.33%.

@@             Coverage Diff              @@
##           ign-gui3     #363      +/-   ##
============================================
- Coverage     67.79%   65.96%   -1.84%     
============================================
  Files            28       29       +1     
  Lines          3118     3191      +73     
============================================
- Hits           2114     2105       -9     
- Misses         1004     1086      +82     

Impacted Files	Coverage Δ
src/plugins/grid_3d/Grid3D.hh	100.00% <ø> (ø)
src/plugins/grid_3d/Grid3D.cc	10.58% <6.33%> (-17.99%)	⬇️

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[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-04-13-fortress-edifice/1367/1