Add set dynamics srv

[joaomoura24]

This adds two ros services for:

• get pybullet object dynamics
• change pybullet object dynamics

Note that we exposed only the dynamic properties that we can both read and write using pybullet.
This was such that the message for getting and changing the parameters would be the same.
If we want to allow the user to get and change different sets of parameters, we have to think about different message system.

[joaomoura24]

I added these changes with @k1631364, so that we can change the parameters online.

We want to extend this to also change the parameters of the robot link.
We can use pybullet to read those provided the robot id and link id.

Do you have any suggestions where you would like this functionality to be placed?

Let's maybe try to get this pull request through and then extend the functionality in another pull request, but you can leave here your thoughts.