Split obstacle_cruise_planner to obstacle stop, slow_down, and cruise, and port them to motion_velocity_planer

[takayuki5168]

Checklist

• I've read the contribution guidelines.
• I've searched other issues and no duplicate issues were found.
• I've agreed with the maintainers that I can plan this task.

Description

Currently, the obstacle_cruise_planner contains the following three dependent features, which makes the design and implementation complicated.

• obstacle stop
• obstacle slow down
• obstacle cruise

Purpose

improve the readability and maintainability of the obstacle stop, slow_down and cruise features by separating the design and implementation

Possible approaches

• Split the obstacle_cruise_planner into the three packages of obstacle stop, slow_down, and cruise.
• Port them to motion_velocity_planner.

Definition of done

The above task list are done.