Add list subcommand

[decwest]

Overview

Add a list subcommand that outputs a list of nodes with logger services enabled.

Development Plan

• Requirements definition: Target only nodes that provide both get_logger_levels and set_logger_levels services. Output the full node name, one per line.
• Decision logic design: Retrieve the node list, obtain the service list for each node, and extract nodes that provide both target services.
• CLI implementation: Add a ros2 log list verb.
• Testing: Prepare nodes with logger services enabled and disabled, and validate the behavior using CLI tests.

[decwest]

@fujitatomoya I have finished implementing the list subcommand, so please take a look when you have time.

The implementation was based on the ros2node list command.

For testing, I implemented a test that launches talker and listener nodes with enable_logger_service=True, along with a no_logger_service node with enable_logger_service=False, and verifies that only talker and listener are listed. I confirmed that this test passes.
In addition, I verified in my robot simulation environment that only nodes with enable_logger_service=True are output promptly, with no noticeable delay.

[fujitatomoya]

@decwest gotcha! thanks, i will take a look later 👍