Update CHANGELOG with 2.7.10 and 2.8.2

[vaszig]

Closes #4843

Changes

• Added the patch release notes for 2.7.10 and 2.8.2

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

• 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 (aff67a0) to head (0506fd9).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4854   +/-   ##
=======================================
  Coverage   96.61%   96.61%           
=======================================
  Files         751      751           
  Lines       25679    25679           
  Branches     3395     3395           
=======================================
  Hits        24809    24809           
  Misses        608      608           
  Partials      262      262           

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