Enable definition of all fields in JointTrajectory message when using test node.

[destogl]

This PR extends test node for JTC to enable definition of all fields in JointTrajectory message when testing a hardware.

This enables velocity, acceleration, and effort only inputs that JTC can handle but test node was unable to until now.
The goal of this work is to simplify testing of a controller for a specific hardware in a specific scenario.

[bmagyar]

little bit of Python learning

[codecov-commenter]

Codecov Report

Merging #389 (ef74a75) into master (e7f9962) will decrease coverage by 5.79%.
The diff coverage is 20.43%.

@@            Coverage Diff             @@
##           master     #389      +/-   ##
==========================================
- Coverage   35.78%   29.98%   -5.80%     
==========================================
  Files         189        7     -182     
  Lines       17570      737   -16833     
  Branches    11592      422   -11170     
==========================================
- Hits         6287      221    -6066     
+ Misses        994      161     -833     
+ Partials    10289      355    -9934     

Flag	Coverage Δ
unittests	29.98% <20.43%> (-5.80%)	⬇️

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

Impacted Files	Coverage Δ
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <ø> (ø)
...ontroller/test/test_load_diff_drive_controller.cpp	12.50% <0.00%> (ø)
diff_drive_controller/src/odometry.cpp	42.16% <11.11%> (ø)
...ive_controller/test/test_diff_drive_controller.cpp	17.62% <12.08%> (ø)
diff_drive_controller/src/speed_limiter.cpp	46.55% <13.33%> (ø)
...troller/include/diff_drive_controller/odometry.hpp	20.00% <20.00%> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	32.67% <24.59%> (ø)
...test/test_load_joint_group_velocity_controller.cpp
...ler/test/test_load_joint_trajectory_controller.cpp
..._state_broadcaster/src/joint_state_broadcaster.cpp
... and 192 more