Ensure that no form variables are created for soft required errors

[sergei-maertens]

Closes #4884

The soft required errors component should have the same behaviour like the content component, as it holds no submission values and is purely client-side behaviour.

Formio itself excludes the content component when looping over a configuration with eachComponent, so we need to add this same logic to our own code since Formio is not aware of our custom component semantics.

In the backend, we extend the behaviour for content components to the softRequiredErrors component to ensure no variables are created in the database either.

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • Checked copying a form
  • Checked import/export of a form
  • Config checks in the configuration overview admin page
  • Problem detection in the admin email digest is handled

• Release management

  • I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • Ran ./bin/makemessages_js.sh
  • Ran ./bin/compilemessages_js.sh

• Dockerfile/scripts

  • Updated the Dockerfile with the necessary scripts from the ./bin folder

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

[sergei-maertens]

I couldn't find existing tests for this and it's so specific/tied to Formio that I don't really know where to start either.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.57%. Comparing base (0dd2174) to head (db8d6fe).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4910   +/-   ##
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  Coverage   96.57%   96.57%           
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  Files         757      757           
  Lines       25750    25750           
  Branches     3383     3383           
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  Hits        24869    24869           
  Misses        616      616           
  Partials      265      265           

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