[PID Controller] Export state interfaces for easier chaining with other controllers

[saikishor]

This PR aims to export some state interfaces from the PID controllers that can be used in cascade with other controllers, this helps in not defining separate parameters for command interfaces (The one exported by the PID controller) and the state interfaces that define the same state as the PID controller, and it simplifies the design of the chained controllers

[codecov]

Codecov Report

Attention: Patch coverage is 63.88889% with 13 lines in your changes missing coverage. Please review.

Project coverage is 80.35%. Comparing base (cdfc0af) to head (e5540ee).
Report is 2 commits behind head on master.

Files	Patch %	Lines
pid_controller/src/pid_controller.cpp	53.57%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1214      +/-   ##
==========================================
- Coverage   80.39%   80.35%   -0.05%     
==========================================
  Files         105      105              
  Lines        9357     9392      +35     
  Branches      821      830       +9     
==========================================
+ Hits         7523     7547      +24     
- Misses       1557     1570      +13     
+ Partials      277      275       -2     

Flag	Coverage Δ
unittests	80.35% <63.88%> (-0.05%)	⬇️

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

Files	Coverage Δ
pid_controller/test/test_pid_controller.hpp	84.78% <100.00%> (+0.16%)	⬆️
..._controller/test/test_pid_controller_preceding.cpp	100.00% <100.00%> (ø)
pid_controller/src/pid_controller.cpp	68.69% <53.57%> (-2.10%)	⬇️

... and 4 files with indirect coverage changes

[christophfroehlich]

Can't we implement this together with ros-controls/ros2_control#1244? Instead of adding this to every chainable controller?

[saikishor]

Can't we implement this together with ros-controls/ros2_control#1244? Instead of adding this to every chainable controller?

@christophfroehlich #1244 is about publishing the interface information to a topic but not exposing as interfaces which is what we need here

[destogl]

Thanks! This looks good!