🚀 Add PID controller 🎉 (backport #434, #975, #899, #1084, #951)

[mergify]

Proposal for a new controller that provides PID functionality.

The controller can be used stand-alone, in a chain.
Measured states can be provided through the topic or state interface, depening on the concrete control arch.
For example, if you are having an external estimator, using topic might be eaiser at first then full integration into ros2_control.

The PR depends the following changes:

• Propose generic messages for commanding and getting states from controllers. control_msgs#69
• [PidROS] Enable interpreting prefix as param prefix. control_toolbox#129

Looking forward for your feedback!

Testing dependencies:

  control_msgs:
    type: git
    url: git@github.com:ros-controls/control_msgs.git
    version: add-generic-msgs-for-controller-references
  control_toolbox:
    type: git
    url: git@github.com:ros-controls/control_toolbox.git
    version: add-option-to-define-prefix-as-param-prefix
  ros2_controllers:
    type: git
    url: git@github.com:StoglRobotics-forks/ros2_controllers.git
    version: add-pid-controller

---

This is an automatic backport of pull request #434 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

Attention: Patch coverage is 84.28875% with 74 lines in your changes missing coverage. Please review.

Project coverage is 86.75%. Comparing base (94149be) to head (0f77bc3).
Report is 2 commits behind head on iron.

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1163      +/-   ##
==========================================
+ Coverage   86.67%   86.75%   +0.08%     
==========================================
  Files          86       91       +5     
  Lines        7412     7831     +419     
  Branches      612      687      +75     
==========================================
+ Hits         6424     6794     +370     
- Misses        759      791      +32     
- Partials      229      246      +17     

Flag	Coverage Δ
unittests	86.75% <84.28%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
pid_controller/test/test_load_pid_controller.cpp	100.00% <100.00%> (ø)
pid_controller/test/test_pid_controller.cpp	100.00% <100.00%> (ø)
..._controller/test/test_pid_controller_preceding.cpp	100.00% <100.00%> (ø)
pid_controller/test/test_pid_controller.hpp	83.14% <83.14%> (ø)
pid_controller/src/pid_controller.cpp	70.79% <70.79%> (ø)

... and 8 files with indirect coverage changes