Servo Node - pause service: check if request is different than current state. (backport #3265)

[mergify]

Description

When using the servo_node from moveit_servo, the service call to /servo_node/pause_servo hangs for a while (sometimes even up to a minute on my machine) when requesting pause = false while the pause status was already false. This behavior can be experienced by running the demo:

ros2 launch moveit_servo demo_ros_api.launch.py

And calling the service:

ros2 service call /servo_node/pause_servo std_srvs/srv/SetBool '{data: false}'

After a while, the following error is logged:

[moveit_servo_demo_container.moveit.ros.move_group.collision_monitor]: Collision monitor could not be started

To avoid this behavior, I propose this change to first check whether the requested pause state is different compared to the current pause state. If not, the response will be returned with the message that nothing is changed since the requested pause stated was already active.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

---

This is an automatic backport of pull request #3265 done by [Mergify](https://mergify.com).

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Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 44.40%. Comparing base (7e1fc53) to head (3d84283).
Report is 1 commits behind head on jazzy.

Files with missing lines	Patch %	Lines
moveit_ros/moveit_servo/src/servo_node.cpp	0.00%	6 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #3348      +/-   ##
==========================================
- Coverage   44.40%   44.40%   -0.00%     
==========================================
  Files         701      701              
  Lines       61857    61863       +6     
  Branches     7493     7494       +1     
==========================================
+ Hits        27464    27466       +2     
- Misses      34225    34230       +5     
+ Partials      168      167       -1     

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