Rewrite mimic joints

[christophfroehlich]

Similar to ros-controls/gazebo_ros2_control#297

The component_parser of the resource_manager now already parses the mimic joint information from the URDF. The old way for defining it in the ros2_control tag is deprecated, see ros-controls/ros2_control#1256.

• This PR uses the info from the hardware_info structure instead of parsing it again.
• From my understanding, mimic means "mimic position". See Add doc page about joint kinematics ros2_control#1497 for the discussion.
• Fixes Why don't you remove _mimic suffix? #96:

$ ros2 control list_hardware_interfaces
command interfaces
        right_finger_joint/position [available] [claimed]
state interfaces
        left_finger_joint/effort
        left_finger_joint/position
        left_finger_joint/velocity
        right_finger_joint/effort
        right_finger_joint/position
        right_finger_joint/velocity
$ ros2 topic echo /joint_states --once
header:
  stamp:
    sec: 61
    nanosec: 200000000
  frame_id: ''
name:
- right_finger_joint
- left_finger_joint
position:
- 0.15
- 0.1500000000000001
velocity:
- 0.0
- -1.1102230246251565e-14
effort:
- 0.0
- 0.0
---

[ahcorde]

Just a small change, LGTM

[saikishor]

LGTM