Workaround for unsupported params file syntax in composable node python launch [Foxy]

[Imaniac230]

Related Issues & PRs

• https://github.com/ouster-lidar/ouster-ros/issues/324
• https://github.com/ouster-lidar/ouster-ros/issues/212#issuecomment-1724075926

Summary of Changes

• This wraps the composable node launch description definitions into a separate function that reads the parameters file directly and extracts parameters for each node.
• The function is then called as an OpaqueFunction launch entity, which allows access to the inner values of LaunchConfiguration entities.
• This also maintains correct support for the user-provided params_file and ouster_ns arguments.
• Added missing ros__parameters key in params for os_image.

Validation

• With default namespace:
  1. Configure parameters in os_sensor_cloud_params.yaml
  2. Colcon build and source workspace
  3. Use the launch file: ros2 launch ouster_ros sensor.composite.launch.py
• With custom namespace:
  1. Configure parameters in os_sensor_cloud_params.yaml with the custom namespace value
  2. Colcon build and source workspace
  3. Use the launch file: ros2 launch ouster_ros sensor.composite.launch.py ouster_ns:=<custom-namespace-value>
  4. The topics in rviz visualization must be changed manually using the custom namespace.
• All other launch files should still continue working correctly.

Target platforms

• ROS2 version -> foxy
• Operating system -> 5.15.0-105-generic #115~20.04.1-Ubuntu