launch_testing documentation improvement plan

[adityapande-1995]

This issue aims to track the PRs focused on improvement launch_testing documentation.

Open PRs :

• Launch testing concept and guide page ros2_documentation#1914 : Adds a concept and guide page to ros2_documentation
• Launch testing examples : ROS focused launch_ros#263 : Add launch_testing examples focused on ROS
• Add a "hello world" style example #532 : Move hello world example from launch_ros to launch
• Add example to record bagfile, launch variable number of nodes launch_ros#269 : Adds example to launch 'n' number of nodes, ros2 bag record demo.
• Moved examples examples#324: Moved examples
• Final batch of examples examples#327 : Final batch of examples

PRs to be opened :

• ros2_documentation page explaining the examples.
• Explain launch_testing.tools

Examples to be written:

• Return local dictionary from generate_test_description(), use those variables ✔️
• Parameterize launch description ✔️
• Launch nodes in the test fixture, kill them later ✔️
• Record data to bagfile, analyse later ✔️
• Parameterized tests(?)
• Turtlebot controller / integration test

Feature requests that came up in PRs :

• Addition of a wait_for_node() function rclpy#823
• Set parameters using rclpy easily, with similar API as AsyncParameterClient class in rclcpp
• Check if a topic is publishing messages, with a timeout : https://github.com/ros2/launch/issues/533 ✔️

[adityapande-1995]

Final batch of examples merged ros2/examples#327, closing this issue.