feat(autoware_carla_interface): add spectator follow script

[mitsudome-r]

Description

• Adds a spectator_follow helper script that locks the CARLA spectator (free) camera onto the ego vehicle, so the in-simulator view chases the car automatically instead of having to be panned manually.
• Connects to the running CARLA server, locates the ego actor by role_name, and updates the spectator transform at a fixed rate. Re-acquires the actor automatically if it is removed/respawned, and retries while waiting for it to spawn.
• Exposes camera framing as CLI flags (--distance, --height, --pitch, --rate) plus connection options (--host, --port, --timeout, --role), with sensible defaults (chase-cam 8 m back, 4 m up, −15° pitch, 30 Hz). Top-down view is supported via --distance 0 --height <h> --pitch -90.
• Documents the new tool in the package README, including usage, the full flag table, and a top-down example.

Related links

Parent Issue:

• Add carla docker compose demo script autoware#7079

How was this PR tested?

• Build: colcon build --packages-select autoware_carla_interface
• Launch CARLA + autoware_carla_interface.launch.xml and confirm the ego vehicle spawns
• Run ros2 run autoware_carla_interface spectator_follow in a separate terminal and verify the CARLA spectator camera tracks the ego vehicle as it drives

Notes for reviewers

None.

Interface changes

None.

Effects on system behavior

None.

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