[#3535] Fix pausing form allows navigating to next step

[vaszig]

Closes #3535

Changes

• Do not always mark a submission step as completed (now even if a form is paused the submission step is saved so the backend treats this as a completed step). This allows the user to navigate to the next step (which in a regular submission is not allowed). OF though can prevent the user from "forgetting" to provide data for a required field in a previous step (we show validation errors).

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

• 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 96.98%. Comparing base (59038e2) to head (b60f3d6).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5666   +/-   ##
=======================================
  Coverage   96.98%   96.98%           
=======================================
  Files         836      836           
  Lines       29953    29953           
  Branches     3875     3875           
=======================================
  Hits        29051    29051           
  Misses        609      609           
  Partials      293      293           

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