Add custom rosdoc2 config for ros2_control metapackage (backport #1484)

[mergify]

rosdoc2 will be used by the build farm to publish API docs on http://docs.ros.org/en/rolling/p/ros2_control/ which is empty now.

• remove doxyfile because it is added to control.ros.org and used here API docs for the whole stack via doxygen control.ros.org#278
• Add custom landing page for rosdoc2: logo, links to control.ros.org
• add rosdoc2 workflow, but only if the relevant files changed

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This is an automatic backport of pull request #1484 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.06%. Comparing base (41723d2) to head (fc46369).

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1589      +/-   ##
==========================================
- Coverage   62.08%   62.06%   -0.02%     
==========================================
  Files         102      102              
  Lines       11775    11775              
  Branches     8447     8444       -3     
==========================================
- Hits         7310     7308       -2     
- Misses        747      748       +1     
- Partials     3718     3719       +1     

Flag	Coverage Δ
unittests	62.06% <ø> (-0.02%)	⬇️

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see 2 files with indirect coverage changes

[christophfroehlich]

I'm stuck here, see ros-infrastructure/rosdoc2#127