[stable7.0] Move changelog license header to a separate file

[backportbot]

Backport of #4374

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.54%. Comparing base (6044915) to head (9066947).
Report is 6 commits behind head on stable7.0.

Additional details and impacted files

@@               Coverage Diff                @@
##             stable7.0    #4375       +/-   ##
================================================
+ Coverage        11.14%   65.54%   +54.40%     
  Complexity         265      265               
================================================
  Files              122       26       -96     
  Lines             5537      772     -4765     
  Branches          1187        0     -1187     
================================================
- Hits               617      506      -111     
+ Misses            4799      266     -4533     
+ Partials           121        0      -121     

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