[#72] Backend validation for addressNL component

[vaszig]

Closes #72

Changes

• Added backend validation for addressNL component

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/compilemessages_js.sh

• 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 96.26%. Comparing base (9b49cd1) to head (7d57946).
Report is 759 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4326      +/-   ##
==========================================
- Coverage   96.26%   96.26%   -0.01%     
==========================================
  Files         731      731              
  Lines       23718    23756      +38     
  Branches     2795     2801       +6     
==========================================
+ Hits        22833    22868      +35     
- Misses        616      617       +1     
- Partials      269      271       +2     

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