Attached Collision Object Transparency

[rr-aiden]

Description

This PR aims to resolve missing functionality from Moveit1 which allowed for attached collision objects to become transparent through the setting of an alpha value in robot_state_visualization.cpp. It also defaults the alpha value to match the Scene Robot Alpha value which was default behaviour for Moveit1.

If this could be backported to Humble it would be much appreciated

Checklist

• [x] 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

[rr-tom-noble]

@rr-aiden Ah my failing tests broke your merge queue jobs :sweat_smile:

Should be good with #3095