Add documentation on ros2_control_node and make lock_memory false by default (backport #1890)

[mergify]

Related to ros-controls/ros2_controllers#1389

---

This is an automatic backport of pull request #1890 done by Mergify.

[mergify]

Cherry-pick of abb4c68 has failed:

On branch mergify/bp/humble/pr-1890
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit abb4c68.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   controller_manager/doc/userdoc.rst

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   controller_manager/src/ros2_control_node.cpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[saikishor]

Waiting for #1896

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.98%. Comparing base (63269d4) to head (4b04da0).
Report is 1 commits behind head on humble.

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1895      +/-   ##
==========================================
- Coverage   63.00%   62.98%   -0.03%     
==========================================
  Files         109      109              
  Lines       12448    12449       +1     
  Branches     8443     8445       +2     
==========================================
- Hits         7843     7841       -2     
- Misses        841      844       +3     
  Partials     3764     3764              

Flag	Coverage Δ
unittests	62.98% <100.00%> (-0.03%)	⬇️

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

Files with missing lines	Coverage Δ
controller_manager/src/ros2_control_node.cpp	67.34% <100.00%> (+0.68%)	⬆️

... and 1 file with indirect coverage changes

[saikishor]

If we are tagging Humble soon, it's better this gets into it

[christophfroehlich]

Thanks