[Python wrapper] add acceleration_scaling_factor to retime_trajectory

[mmurooka]

Description

• Add acceleration_scaling_factor argument to the retime_trajectory method of Python MoveGroupCommander.
• Set default value of velocity_scaling_factor and acceleration_scaling_factor to 1. Same with raw C++ function:
  https://github.com/ros-planning/moveit/blob/master/moveit_core/trajectory_processing/include/moveit/trajectory_processing/iterative_time_parameterization.h#L55-L56

Example code:

plan_retimed = self.move_group.retime_trajectory(
    reference_state, plan,
    # velocity_scaling_factor=1.0, # can be omitted if 1.0
    acceleration_scaling_factor=0.1) # this argument becomes supported by this PR.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extended the tutorials / documentation, if necessary reference
• Include a screenshot if changing a GUI
• Document API changes relevant to the user in the moveit/MIGRATION.md notes
• Created tests, which fail without this PR reference
• Decide if this should be cherry-picked to other current ROS branches
• While waiting for someone to review your request, please consider reviewing another open pull request to support the maintainers

[welcome]

Thanks for helping in improving MoveIt!

[felixvd]

I haven't tested it myself, but I see nothing wrong with this. I'm all for exposing more variables in Python.

[v4hn]

This was already merged as part of #1508