feat: Thread configuration prototype

[smorita-esol]

This is a prototype implementation of RCL for discussion about the thread configuration feature to receive and apply a set of scheduling parameters for the threads controlled by the ROS 2 executor.

Our basic idea is as below.

1. Implement a new class rclcpp::thread and modify rclcpp to use it. This class has the same function set as the std::thread but also additional features to control its thread attributions.
2. Modify the rcl layer to receive a set of scheduling parameters. The parameters are described in YAML format and passed via command line parameters, environment variables, or files.
3. the rclcpp reads the parameters from rcl and applies them to each thread in the thread pool. *1 *1. the current implementation uses them only for the Multithread Executor.

[k-yokoyama-esol]

This issue is obsolete.
Another pull request continues the discussion.
ros2#1075