[jazzy] Add missing public dependency on fmt library

[traversaro]

The fmt public dependency was added in the C++ code in #410, but without properly declaring the dependency in CMake and package.xml . The issue in the ros2-master branch was fixed by #391, but that PR was not backported to the jazzy branch.

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[mergify]

@traversaro, all pull requests must be targeted towards the ros2-master development branch.
Once merged into ros2-master, it is possible to backport to jazzy, but it must be in ros2-master
to have these changes reflected into new distributions.

[traversaro]

@traversaro, all pull requests must be targeted towards the ros2-master development branch. Once merged into ros2-master, it is possible to backport to jazzy, but it must be in ros2-master to have these changes reflected into new distributions.

Hello bot, the ros2-master branch already contains that fix, that however was contained in a PR that was not backported.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.23%. Comparing base (dd5a768) to head (2b94696).

Additional details and impacted files

@@           Coverage Diff           @@
##            jazzy     #435   +/-   ##
=======================================
  Coverage   76.23%   76.23%           
=======================================
  Files          29       29           
  Lines        2066     2066           
  Branches      125      125           
=======================================
  Hits         1575     1575           
  Misses        420      420           
  Partials       71       71           

Flag	Coverage Δ
unittests	76.23% <ø> (ø)

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[christophfroehlich]

Thanks