Fix/controller yaml defaults

[Eldgar]

Fix

When the user skips “Edit Selected,” Setup Assistant dropped
action_ns and default from moveit_controllers.yaml (see #3434).
This patch adds fallback values:

action_ns: follow_joint_trajectory
default: true

Test

Adds InjectedDefaultsWhenBlank to test_controllers.cpp to verify
those keys are always present.

Fixes #3434

[mergify]

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

[mergify]

Please target the main branch for development, we will backport the changes to jazzy for you if approved and if they don't break API.

[mergify]

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

[mikeferguson]

I've triggered the CI - looks like the linter isn't happy with a bit of the whitespace

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Project coverage is 46.23%. Comparing base (fb34bff) to head (14580fe).

Files with missing lines	Patch %	Lines
...etup_controllers/src/moveit_controllers_config.cpp	92.31%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3478      +/-   ##
==========================================
+ Coverage   46.23%   46.23%   +0.01%     
==========================================
  Files         720      720              
  Lines       62713    62738      +25     
  Branches     7591     7595       +4     
==========================================
+ Hits        28991    29003      +12     
- Misses      33555    33567      +12     
- Partials      167      168       +1     

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