[featherstone] Publish JointFeedback forces.

[Fixit-Davide]

🎉 New feature

Related to the PR: https://github.com/gazebosim/gz-sim/pull/2369

Partially solves: https://github.com/gazebosim/gz-sim/issues/883

Summary

Allow the GetJointForce() method in bullet-featherston to return the joint feedback Force and not 0. This allow the joint_state_publisher to publish data containing the force field.

Test it

• Launch gz sim --physics-engine gz-physics-bullet-featherstone-plugin lift_drag.sdf simulation.
• Send a command to the model (gz topic -t "/model/lift_drag_demo_model/joint/rod_1_joint/cmd_force" -m gz.msgs.Double -p "data: 0.8").
• Echo the topic: gz topic -e -t /world/lift_drag/model/lift_drag_demo_model/joint_state

  Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

[iche033]

CI picked up a few cpplint warnings:

  /github/workspace/bullet-featherstone/src/JointFeatures.cc:87:  Line ends in whitespace.  Consider deleting these extra spaces.  [whitespace/end_of_line] [4]
  /github/workspace/bullet-featherstone/src/JointFeatures.cc:90:  Lines should be <= 80 characters long  [whitespace/line_length] [2]
  /github/workspace/bullet-featherstone/src/JointFeatures.cc:95:  Lines should be <= 80 characters long  [whitespace/line_length] [2]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.67%. Comparing base (92e02c3) to head (9aee181). Report is 21 commits behind head on gz-physics7.

:exclamation: Current head 9aee181 differs from pull request most recent head beaacc7

Please upload reports for the commit beaacc7 to get more accurate results.

Files	Patch %	Lines
bullet-featherstone/src/JointFeatures.cc	0.00%	24 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## gz-physics7 #628 +/- ## =============================================== + Coverage 78.32% 78.67% +0.34% =============================================== Files 140 140 Lines 8069 8158 +89 =============================================== + Hits 6320 6418 +98 + Misses 1749 1740 -9 ```

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[Fixit-Davide]

Any changes needed in order to merge? I can write the test for https://github.com/gazebosim/gz-sim/pull/2369 afterward.

[iche033]

I'll go ahead and merge this first