Add PID controller to control joint using effort (backport #294)

[mergify]

Change :

• Added PID Implementation
• Added effort-based Position Controller
• Added effort-based Velocity Controller

Motivation :

The primary goal behind these changes is to model the behavior of a low-level joint controller more accurately, rather than relying on workarounds within the physics engine. Additionally, addressing some limitations related to closed-loop kinematic chains using Position and Velocity control interfaces is another objective. The PR could maybe also solve this issue #240

Change in usage :

The usage remains largely the same as before, with one key difference. If you declare parameters kp, ki, or kd using the command_interface for Position or Velocity, the controller will apply effort to the joint based on the specified PID gains instead of directly setting the joint position or velocity.

Usage exemple :

Here’s an example of the new usage for controlling the velocity of a joint using an Effort PID:

    <ros2_control name="my_GazeboSystem" type="system">
    
      <hardware>
        <plugin>gazebo_ros2_control/GazeboSystem</plugin>
      </hardware>
      
      <joint name="my_joint">
        
        <param name="kp">10</param>
        <param name="ki">2</param>
        <param name="kd">0.1</param>
        <param name="max_integral_error">1000</param>


        
        <command_interface name="velocity">
          <param name="min">0</param>
          <param name="max">2</param>
        </command_interface>

        
        <state_interface name="position">
          <param name="initial_value">0</param>
        </state_interface>

        <state_interface name="velocity"/>
        <state_interface name="effort"/>

      </joint>

    </ros2_control>

The second example retains the original behavior, where a Velocity controller sets the velocity of the joint in the physics engine :

    <ros2_control name="my_GazeboSystem" type="system">
    
      <hardware>
        <plugin>gazebo_ros2_control/GazeboSystem</plugin>
      </hardware>
      
      <joint name="my_joint">
        
        
        <command_interface name="velocity">
          <param name="min">0</param>
          <param name="max">2</param>
        </command_interface>

        
        <state_interface name="position">
          <param name="initial_value">0</param>
        </state_interface>

        <state_interface name="velocity"/>
        <state_interface name="effort"/>

      </joint>

    </ros2_control>

---

This is an automatic backport of pull request #294 done by [Mergify](https://mergify.com).

[mergify]

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Changes to be committed:
	modified:   doc/index.rst
	modified:   gazebo_ros2_control/CMakeLists.txt
	modified:   gazebo_ros2_control/include/gazebo_ros2_control/gazebo_system.hpp
	modified:   gazebo_ros2_control/include/gazebo_ros2_control/gazebo_system_interface.hpp
	modified:   gazebo_ros2_control/package.xml
	modified:   gazebo_ros2_control_demos/CMakeLists.txt
	new file:   gazebo_ros2_control_demos/config/cart_controller_position.yaml
	new file:   gazebo_ros2_control_demos/examples/example_position_pid.cpp
	new file:   gazebo_ros2_control_demos/launch/vertical_cart_example_position_pid.launch.py
	new file:   gazebo_ros2_control_demos/launch/vertical_cart_example_velocity_pid.launch.py
	new file:   gazebo_ros2_control_demos/urdf/test_vertical_cart_position_pid.xacro.urdf
	new file:   gazebo_ros2_control_demos/urdf/test_vertical_cart_velocity_pid.xacro.urdf

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   gazebo_ros2_control/src/gazebo_system.cpp

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