[CM] Add controller_manager activity topic

[saikishor]

As discussed in the ros2_control WG meeting on 15th Jan 2025

I've added a topic to the CM inorder to publish information on changes in the CM. This is quite useful to have when developing applications that need to be dynamic enough with the changes in CM. Right now, the only way is to spam the CM with lot of service requests.

It should look something like the below

---
header:
  stamp:
    sec: 1737128088
    nanosec: 39885323
  frame_id: ''
controllers:
- name: forward_position_controller
  state:
    id: 2
    label: inactive
- name: position_controller
  state:
    id: 3
    label: active
- name: joint2_position_controller
  state:
    id: 3
    label: active
- name: joint1_position_controller
  state:
    id: 3
    label: active
- name: joint_state_broadcaster
  state:
    id: 3
    label: active
hardware_components:
- name: RRBot
  state:
    id: 3
    label: active
---

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.37%. Comparing base (f8c03cc) to head (e975db7).

Files with missing lines	Patch %	Lines
...ontroller_manager/test/test_controller_manager.cpp	90.00%	0 Missing and 3 partials ⚠️
controller_manager/src/controller_manager.cpp	96.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2006      +/-   ##
==========================================
+ Coverage   89.35%   89.37%   +0.01%     
==========================================
  Files         130      130              
  Lines       14576    14640      +64     
  Branches     1258     1265       +7     
==========================================
+ Hits        13024    13084      +60     
+ Misses       1088     1085       -3     
- Partials      464      471       +7     

Flag	Coverage Δ
unittests	89.37% <93.75%> (+0.01%)	⬆️

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

Files with missing lines	Coverage Δ
.../include/controller_manager/controller_manager.hpp	100.00% <ø> (ø)
hardware_interface/src/resource_manager.cpp	75.15% <100.00%> (+0.12%)	⬆️
controller_manager/src/controller_manager.cpp	76.58% <96.66%> (+0.42%)	⬆️
...ontroller_manager/test/test_controller_manager.cpp	95.87% <90.00%> (-0.23%)	⬇️

... and 4 files with indirect coverage changes

[christophfroehlich]

great addition. Should we also add a publisher section here describing this?
https://control.ros.org/rolling/doc/ros2_control/controller_manager/doc/userdoc.html#subscribers

[saikishor]

great addition. Should we also add a publisher section here describing this?
https://control.ros.org/rolling/doc/ros2_control/controller_manager/doc/userdoc.html#subscribers

Actually, I want to document all the Services and Publishers from the controller manager. I don't know if I have to do it in this PR or a separate PR. What's your opinion @christophfroehlich

[Maverobot]

Is it better to call it on_switch_callback_ instead?

[christophfroehlich]

great addition. Should we also add a publisher section here describing this?
https://control.ros.org/rolling/doc/ros2_control/controller_manager/doc/userdoc.html#subscribers

Actually, I want to document all the Services and Publishers from the controller manager. I don't know if I have to do it in this PR or a separate PR. What's your opinion @christophfroehlich

please add the docs for this new publisher with this PR.