bug fix: no transparency in collision scenes on rviz

[samialperen]

Description

On ROS humble and rviz2, I realized that collision scenes are not transparent even if their alpha value is not 1.0
This MR fixes this bug.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (636b988) 50.50% compared to head (d366a61) 50.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2242      +/-   ##
==========================================
- Coverage   50.50%   50.50%   -0.00%     
==========================================
  Files         386      386              
  Lines       31731    31732       +1     
==========================================
  Hits        16022    16022              
- Misses      15709    15710       +1     

Impacted Files	Coverage Δ
..._plugin_render_tools/src/planning_scene_render.cpp	0.00% <0.00%> (ø)

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[samialperen]

@henningkayser let me know if you need more information from my side to merge this change.

[dhood]

@JafarAbdi would you be willing to backport this to humble, please?

[samialperen]

@JafarAbdi I do not see this being backported to humble yet. https://github.com/moveit/moveit2/blob/humble/moveit_ros/visualization/rviz_plugin_render_tools/src/planning_scene_render.cpp#L112

When do you think it would be possible? 🤔