[#5074] Transform data for selectboxes in the registrations (variables tab)

[vaszig]

Closes #5074

Changes

• Add checkbox for transforming the data to a list for Objects API and JSON dump registations (variables tab)

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.74%. Comparing base (a517a16) to head (9e2ee4b).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5130   +/-   ##
=======================================
  Coverage   96.74%   96.74%           
=======================================
  Files         779      779           
  Lines       26774    26787   +13     
  Branches     3483     3486    +3     
=======================================
+ Hits        25903    25916   +13     
  Misses        607      607           
  Partials      264      264           

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[sergei-maertens]

I'd appreciate some storybook stories for the selectboxes component type and alternative UI 😬