Add per composable node log_level support

[penww]

Description

Fixes # (ros2/rclcpp#3091)

Is this user-facing behavior change?

No, this change add new parameter for ComposableNode, not affect the existing functions.

Did you use Generative AI?

Yes, partially with Claude Sonnet 4.6.

Additional Information

Example for per component log level feature enabled:

def generate_launch_description():
    return LaunchDescription([ComposableNodeContainer(
        name='component_demo_container',
        namespace='',
        package='rclcpp_components',
        executable='component_container',
        composable_node_descriptions=[
            ComposableNode(
                package='<PKG>',
                plugin='<PLUGIN>',
                log_level='DEBUG',  # component log level
            ),
        ],
        arguments=['--ros-args', '--log-level', 'INFO'],  # container log level
    )])

Related PR: ros2/rclcpp#3092, ros2/ros2cli#1212

[fujitatomoya]

test would be ideal too.

[fujitatomoya]

this fallback is NOT great for the user application. if user sets typos log_level='debig', it silently sets it to UNSET and the user will not be notified configuration gone wrong. i think that this behavior is actually worse then raising the exception, what do you think? i say, we should enforce the check and return error would be better. and again this should be done with rclpy get_logging_severity_from_string?

[fujitatomoya]

should be rcl_interfaces.msg.LoggerLevel.

[fujitatomoya]

docstring does not mention about this string though... we should add it to the help docstring?