refactor(vehicle): delegate vehicle interface launch to vehicle_launch pkg

[Autumn60]

Description

Adds a string argument vehicle_launch_mode to tier4_vehicle_launch's vehicle.launch.xml to choose how vehicle-related launch is done.

Value	Behavior
vehicle_interface (default)	Legacy: this launch file includes vehicle_interface.launch.xml when launch_vehicle_interface is true.
vehicle	Includes the vehicle package's vehicle.launch.xml and passes launch_vehicle_interface (and other args). The vehicle package decides whether to start vehicle_interface and can run vehicle-specific logic (e.g. SteeringReport → JointState for articulated vehicles) with or without it.

This enables launching vehicle-specific functionality without vehicle_interface, which is useful for articulated vehicles and especially for simulation, where vehicle_interface is usually not needed.

How was this PR tested?

• vehicle_launch_mode="vehicle_interface": behavior matches the previous implementation.
• vehicle_launch_mode="vehicle": vehicle package's vehicle.launch.xml is included and receives the intended arguments.

Notes for reviewers

None.

Effects on system behavior

• Backward compatible: Default is vehicle_interface; existing callers and vehicle packages require no change.
• Opt-in: Set vehicle_launch_mode="vehicle" to use a vehicle package's vehicle.launch.xml. That package must provide launch/vehicle.launch.xml and handle launch_vehicle_interface as needed.

[github-actions]

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