Ensure that planner id is set

[sjahr]

Description

The planner id in the motion plan response does not seem to be set by our planner plugins (I tested stomp and OMPL). This fixes it plugin agnostic without overwriting whatever the plugin sets.

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 (052c217) 50.57% compared to head (de07882) 50.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2202      +/-   ##
==========================================
- Coverage   50.57%   50.56%   -0.00%     
==========================================
  Files         387      387              
  Lines       31740    31740              
==========================================
- Hits        16048    16045       -3     
- Misses      15692    15695       +3     

see 2 files with indirect coverage changes

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