Sim payload camera bridge should support explicit compressed-source transport

[ethayu]

Summary

The sim payload camera path only publishes a raw upstream source (camera_source) from the Gazebo bridge. If a fleet requests camera_input_transport: compressed for a payload vehicle, CameraNode subscribes to camera_source/compressed, which does not exist in sim.

A launch-side guard now normalizes sim payload input transport back to raw, so the stack stays healthy. That fixes the runtime breakage, but it also means sim still cannot model a true compressed upstream camera source.

Repro

1. Launch a sim payload fleet with a payload vehicle configured as camera_input_transport: compressed.
2. Observe that Gazebo only provides /.../camera_source and /.../camera_info_source.
3. CameraNode waits on camera_source/compressed, and /camera never gets frames unless launch coerces the transport to raw.

Current behavior

• Sim payload bridge publishes raw image + camera info only.
• Launch now coerces sim payload camera_input_transport from compressed/both to raw.
• Downstream /camera/compressed can still be synthesized by CameraNode when subscribers exist.

Desired behavior

One of these should become the long-term contract:

• either sim explicitly supports a compressed upstream payload source as well,
• or the config/schema/docs make it impossible to request compressed upstream transport for sim payloads.