quietly use backward_cpp/ros if available

[v4hn]

This is plain convenient and you always need it when you did not explicitly add it.

Follow @tylerjw's initiative to add it to MoveIt2: moveit/moveit2#794

The downside (at least on my system) is that the cmake config for the package is not implemented correctly and yields this warning for each find_package call:

CMake Warning (dev) at /usr/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:426 (message):
  The package name passed to `find_package_handle_standard_args` (Backward)
  does not match the name of the calling package (backward_ros).  This can
  lead to problems in calling code that expects `find_package` result
  variables (e.g., `_FOUND`) to follow a certain pattern.

[rhaschke]

Looks like a useful package, indeed. It won't enter release builds though, thus no more information will be available for users to report in issues...

[rhaschke]

Looks like a useful package, indeed. It won't enter release builds though, thus no more information will be available for users to report in issues...

[tylerjw]

I get these same cmake warnings in ROS2 locally some times: pal-robotics/backward_ros#10

I have not debugged it further to figure out why or how to fix this.

[codecov]

Codecov Report

Merging #2988 (902b518) into master (9bfb2c7) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2988      +/-   ##
==========================================
+ Coverage   61.57%   61.59%   +0.02%     
==========================================
  Files         370      370              
  Lines       33163    33163              
==========================================
+ Hits        20418    20422       +4     
+ Misses      12745    12741       -4     

Impacted Files	Coverage Δ
...eit_ros/manipulation/pick_place/src/pick_place.cpp	88.58% <0.00%> (-3.80%)	⬇️
...ipulation/pick_place/src/manipulation_pipeline.cpp	71.91% <0.00%> (-2.47%)	⬇️
...dl_kinematics_plugin/src/kdl_kinematics_plugin.cpp	78.28% <0.00%> (+0.38%)	⬆️
...meterization/work_space/pose_model_state_space.cpp	80.00% <0.00%> (+0.59%)	⬆️
...on/pick_place/src/approach_and_translate_stage.cpp	74.69% <0.00%> (+0.64%)	⬆️
..._interface/src/detail/constrained_goal_sampler.cpp	76.48% <0.00%> (+1.97%)	⬆️
.../ompl_interface/src/detail/constrained_sampler.cpp	60.98% <0.00%> (+17.08%)	⬆️

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