Add an option to skip interpolation in the joint trajectory controller

[AndyZe]

This should be useful if a user has a trajectory that is already interpolated to a fine degree, or if the low-level controllers just don't handle fine waypoint spacing well.

To use, just set the parameter in the yaml file. If the parameter is unset, it defaults to the previous method (which is spline-based). The default spline-based method doesn't obey joint limits (position/vel/accel/jerk), which is another reason to use this.

panda_arm_controller:
  ros__parameters:
    command_interfaces:
      - position
      - velocity
      - acceleration
    state_interfaces:
      - position
      - velocity
      - acceleration
    joints:
      - panda_joint1
      - panda_joint2
      - panda_joint3
      - panda_joint4
      - panda_joint5
      - panda_joint6
      - panda_joint7
    interpolation_method: none   # (or "splines")
    joint_limits:
      panda_joint1:
        has_velocity_limits: true
        max_velocity: 2.1750
        has_acceleration_limits: true
        max_acceleration: 3.75
      panda_joint2:
        ...

[destogl]

Shouldn't we check this before calling sample in the update method?

What I understand, we will anyway have also ruckig based interpolation this means that we would need some base class for interpolations. If so we can then just decide at the begining in the configure which interpolation should be used and if non is used then we have default "passthrough" interpolation.

[destogl]

this should also reduce number of checks.

[AndyZe]

I don't think Ruckig is going to be a drop-in replacement for the spline interpolation that's currently there. It requires position/vel/accel inputs. What if there is only a position interface active? Then Ruckig will not have vel/accel input. So we will often still need to run some type of interpolation before Ruckig.

I'm trying to figure out the logic re. your comment on update...

[mergify]

This pull request is in conflict. Could you fix it @AndyZe?

[bmagyar]

Thanks!

[destogl]

Few comments to increase maintainability and clarity in the code. Sorry, guys if I am starting to be too picky, and please tell me if I am drifting away in my requests/concerns.

[destogl]

Thanks for all the follow-ups!