Remove added path index from function signatures

[sjahr]

Description

• Add added_path_index to MotionPlanResponse
• Cleanup PlanRequestAdapter function signatures
• Cleanup PlanningPipeline function signatures

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 (4476fb6) 50.72% compared to head (12e0f4d) 50.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2285      +/-   ##
==========================================
- Coverage   50.72%   50.71%   -0.00%     
==========================================
  Files         386      386              
  Lines       31914    31914              
==========================================
- Hits        16184    16181       -3     
- Misses      15730    15733       +3     

see 1 file with indirect coverage changes

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