Add Tf publishing to AckermannSteering system

[andyblarblar]

🎉 New feature

Closes #1573

Summary

Previously, the AckermannSteering system plugin did not publish tf alongside odometry, unlike the DiffDrive controller. This ment that when used with ROS, no odom->base_footprint was generated, preventing its use with SlamToolbox. This PR ports that DiffDrive tf publishing to the AckermannSteering controller, as well as the appropriate docs.

Here's ackermann in use with slam-toolbox post fix:

Checklist

• Signed all commits for DCO
• Added tests
• 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

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[ahcorde]

Linters are failing https://github.com/gazebosim/gz-sim/runs/7208392386?check_suite_focus=true

[andyblarblar]

I've implemented the suggestions and delt with the linter and CI. The fix is still fully working so it should be all set.

[ahcorde]

can you add a test to check that the tf topic is generating data ?

[codecov]

Codecov Report

Merging #1576 (afaf2d8) into ign-gazebo6 (d6e69d0) will increase coverage by 0.00%.
The diff coverage is 83.33%.

❗ Current head afaf2d8 differs from pull request most recent head 82ab5e0. Consider uploading reports for the commit 82ab5e0 to get more accurate results

@@             Coverage Diff              @@
##           ign-gazebo6    #1576   +/-   ##
============================================
  Coverage        64.02%   64.03%           
============================================
  Files              317      317           
  Lines            25649    25666   +17     
============================================
+ Hits             16422    16435   +13     
- Misses            9227     9231    +4     

Impacted Files	Coverage Δ
...rc/systems/ackermann_steering/AckermannSteering.hh	100.00% <ø> (ø)
src/systems/diff_drive/DiffDrive.hh	100.00% <ø> (ø)
...rc/systems/ackermann_steering/AckermannSteering.cc	85.67% <76.47%> (-0.50%)	⬇️
src/Util.cc	92.53% <100.00%> (ø)

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[andyblarblar]

Test added and passed.

[ahcorde]

Uhm, focal is not happy https://github.com/gazebosim/gz-sim/runs/7385398190?check_suite_focus=true

[andyblarblar]

Uhm, focal is not happy https://github.com/gazebosim/gz-sim/runs/7385398190?check_suite_focus=true

Focal ran fine, that's bionic failing there. It looks like the protobuf generated repeated_ptr_feild type doesn't have an operator[] on bionic, which seems odd to me. Does the bionic environment use a different protobuf version than focal? I would imagine gazebo has set dependencies but I cannot think of another cause for this compile error.

Edit: looking at past CI runs, bionic passed before the last commit. None of the lines I changed should have any effect on the protobuf API, so it looks like this is likely a change in the CI between the two commits.

Edit Edit: My bad for all the comments, it looks like bionic is using libprotobuf-dev 3.0.0, vs focals 3.6.1. The operator[] was added in 3.2, hence the build failures. It looks like it's just a wrapper around .get(index), so swapping the functions should solve the issue. I'll submit a fix later today

[andyblarblar]

The test failing on CI also fails on ign-gazebo6 for me, and contains no refrence to the files changed in this PR, so it seems to be a seprerate issue.

[chapulina]

LGTM, thanks!

Addressed