📝 [#3283] Document registration backend migration procedure

[sergei-maertens]

Closes #3283

Changes

• Documented how to migrate registration options
• Updated comments to reflect real scheduled version for removal

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 96.61%. Comparing base (99d8c52) to head (29c3bf4).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4941   +/-   ##
=======================================
  Coverage   96.61%   96.61%           
=======================================
  Files         760      760           
  Lines       25817    25817           
  Branches     3382     3382           
=======================================
  Hits        24944    24944           
  Misses        608      608           
  Partials      265      265           

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[vaszig]

There is one more place left which (if I am not wrong) needs update.

https://github.com/open-formulieren/open-forms/blob/master/src/openforms/registrations/contrib/objects_api/typing.py#L41

[sergei-maertens]

There is one more place left which (if I am not wrong) needs update.

https://github.com/open-formulieren/open-forms/blob/master/src/openforms/registrations/contrib/objects_api/typing.py#L41

Nice catch, I've updated it!