[Feature request]: Support top-view thumbnail generator in Gz Harmonic

Before proceeding, is there an existing issue or discussion for this?

• I have done a search for similar issues and discussions.

Description

The thumbnail generator is helpful for creating thumbnails at a fixed scale, to populate top-down editors like traffic-editor with models.

The goal would be to

• migrate the legacy thumbnail generator implementation (supports Gazebo classic only) and support Gazebo Harmonic onwards
• update documentation on how to generate thumbnails

A good reference would also be the upstream gazebo model prop shop system plugin, that is used for generating thumbnails before uploading models onto Fuel.

Relevant links and references:

• legacy implementation for gazebo classic: https://github.com/open-rmf/rmf_simulation/blob/humble/rmf_building_sim_gz_classic_plugins/src/thumbnail_generator.cpp
• generated thumbnails: https://github.com/open-rmf/rmf_traffic_editor/tree/main/rmf_traffic_editor_assets
• legacy instructions: https://github.com/open-rmf/rmf_traffic_editor/tree/main/rmf_traffic_editor#generating-custom-thumbnails
• gz model prop shop plugin as a reference: https://github.com/gazebosim/gz-sim/blob/gz-sim9/src/systems/model_photo_shoot/ModelPhotoShoot.cc
• gz model prop shop world as a reference: https://github.com/gazebosim/gz-sim/blob/gz-sim9/examples/worlds/model_photo_shoot.sdf

Implementation Considerations

No response

Alternatives

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Additional information

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Start with rmf_building_sim_gz_classic_plugins/src/thumbnail_generator.cpp and the legacy thumbnail-generation instructions, then compare them with gz-sim9/src/systems/model_photo_shoot/ModelPhotoShoot.cc and examples/worlds/model_photo_shoot.sdf. Done means a thumbnail generator works with Gazebo Harmonic onwards and the documentation explains how to generate thumbnails.