Prepare patch release 2.8.4

[robinmolen]

Part of #5055

Changes

• Updated changelog
• Bumped version

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 96.55%. Comparing base (d9bf128) to head (0bf3c9b).
Report is 2 commits behind head on stable/2.8.x.

Additional details and impacted files

@@              Coverage Diff              @@
##           stable/2.8.x    #5056   +/-   ##
=============================================
  Coverage         96.55%   96.55%           
=============================================
  Files               746      746           
  Lines             25318    25318           
  Branches           3342     3342           
=============================================
  Hits              24446    24446           
  Misses              605      605           
  Partials            267      267           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sergei-maertens]

There will be more changelog entries of course :)

[sergei-maertens]

Bugfix releases should basically have "Fixed ..." for every changelog entry. Additional CI fixes etc. can be omitted, it's not useful information to people that want to know which bugs are fixed (because they want to know if their problems have been solved).

Suggested change

	* [:backend:`5035`] Removed non-existing data shown in components variables and
	legacy Objects API submission data.
	* Fixed broken links in redis documentation.
	* Pinned Github actions runners to Ubuntu version 22.04.
	* Upgraded the Django framework to version 4.2.18.
	* Updated eHerkenning documentation.
	* [:backend:`5035`] Fixed the legay Objects API registration including fields from other steps in the submitted data.
	* Applied the latest Django security patches.