Improve pnp vacuum example

[cpr-fer]

The pick_and_place_vacuum example seems to offer not much over the other pick_and_place example. Ideas for improving it could include:

• [x] Use different frames for the trays. (done by #33)
• [ ] Fix the velocity scaling, it appears to not change anything (WIP with #34)
• [x] Gripper client wont work with the changed class structure (fixed by 043d732)
• [x] Readme requires more info regarding frames (fixed by 3908206)
• [ ] Dynamic frames, e.g. detection via camera?
• [ ] Include different pick and place patterns and rotate through them

[cpr-fer]

Regarding point 2: It appears as computeCartesianPath does not take the velocity and acceleration limits into account. Instead you have to manually change the timing of the trajectory.

See the following link for more info: https://ceti.pages.st.inf.tu-dresden.de/robotics/howtos/CartesianMovementSpeed.html

Regarding how to scale the start points correctly: https://github.com/ros-planning/moveit2/blob/humble/moveit_core/trajectory_processing/include/moveit/trajectory_processing/time_parameterization.h