[Moveitpy] new planning scene message

[JensVanhooydonck]

Description

Added the new_planning_scene_message function to the planning_scene_monitor in moveitpy.

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
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