Get rid of "std::endl"

[ParthasarathyBana]

As described in PR #875, as a solution to the good first issue, this PR removes std::endl in all the code files in moveit2 repo and replaces them with '\n'. As mentioned here, removing std::endl is considered to be a better code practice as it improves performance. More information of when to use std::endl and when not to use, can be found here

[mergify]

This pull request is in conflict. Could you fix it @ParthasarathyBana?

[tylerjw]

This looks good. We'll see if it passes CI first.

[codecov]

Codecov Report

Merging #918 (baa64ba) into main (4cbd1a7) will increase coverage by 0.03%.
The diff coverage is 12.20%.

@@            Coverage Diff             @@
##             main     #918      +/-   ##
==========================================
+ Coverage   57.89%   57.92%   +0.03%     
==========================================
  Files         310      310              
  Lines       26072    26067       -5     
==========================================
+ Hits        15093    15096       +3     
+ Misses      10979    10971       -8     

Impacted Files	Coverage Δ
...ore/backtrace/include/moveit/backtrace/backtrace.h	0.00% <0.00%> (ø)
..._core/collision_detection/src/collision_matrix.cpp	42.67% <0.00%> (ø)
...on_distance_field/collision_distance_field_types.h	59.41% <ø> (ø)
...istance_field/src/collision_env_distance_field.cpp	54.06% <ø> (ø)
moveit_core/planning_scene/src/planning_scene.cpp	49.52% <0.00%> (ø)
moveit_core/robot_model/src/joint_model_group.cpp	60.86% <0.00%> (ø)
moveit_core/robot_model/src/robot_model.cpp	74.82% <0.00%> (+0.19%)	⬆️
moveit_core/robot_state/src/conversions.cpp	64.76% <0.00%> (ø)
.../ompl_interface/src/detail/constraints_library.cpp	0.00% <0.00%> (ø)
...ners/ompl/ompl_interface/src/detail/goal_union.cpp	0.00% <0.00%> (ø)
... and 10 more

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