Respect robot alpha value in trail trajectory visual

[flbeck]

Description

The motion planning plugin in RViz does not respect the alpha values for attached bodies when visualizing the trail of the planned path. The alpha values of the trail are only updated if the attached body color is changed at a later point.

Updating the attached body color upon creation of the trail fixes this problem. The same thing applies to drawing the robot along the planned path which is handeled in the update function.

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

[sea-bass]

Thank you!

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 46.23%. Comparing base (bb2eb75) to head (f3ddd4f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ugin_render_tools/src/trajectory_visualization.cpp	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3353      +/-   ##
==========================================
+ Coverage   45.84%   46.23%   +0.39%     
==========================================
  Files         717      717              
  Lines       62573    62596      +23     
  Branches     7564     7564              
==========================================
+ Hits        28680    28932     +252     
+ Misses      33726    33498     -228     
+ Partials      167      166       -1     

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