Add empty set_atomically parameter service (backport #354)

[mergify[bot]]

This is an automatic backport of pull request #354 done by Mergify.

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[codecov-commenter]

Codecov Report

Merging #358 (c81bdae) into iron (2648503) will increase coverage by 0.35%. The diff coverage is 95.55%.

@@            Coverage Diff             @@
##             iron     #358      +/-   ##
==========================================
+ Coverage   69.20%   69.56%   +0.35%     
==========================================
  Files          16       16              
  Lines        2715     2760      +45     
  Branches      765      766       +1     
==========================================
+ Hits         1879     1920      +41     
- Misses        450      453       +3     
- Partials      386      387       +1     

Impacted Files	Coverage Δ
...lc_parameter/src/rclc_parameter/parameter_server.c	83.10% <95.55%> (+0.68%)	:arrow_up:

... and 1 file with indirect coverage changes

[JanStaschulat]

@pablogs9 @Acuadros95 the ci pipeline on OSRF build farm is not triggered for Rolling and Iron for all of the pending pull requests. Do you have any idea what else to check?

created an issue for this: https://github.com/ros2/rclc/issues/366